Method of forming resist pattern

ABSTRACT

A method of forming a resist pattern, comprising: a step of forming a resist film on a substrate using a resist composition containing a base component (A) which exhibits decreased solubility in an organic solvent under action of acid and an acid-generator component (B) which generates acid upon exposure; a step of subjecting the resist film to exposure; a step of patterning the resist film by a negative-tone development using a developing solution containing the organic solvent to form a resist pattern; a step of applying a coating material to the resist pattern, thereby forming a coating film; a step of performing a thermal treatment at a temperature lower than the softening point of the resist pattern, thereby heat shrinking the coating film to narrow an interval between the resist pattern; and a step of removing the coating film.

TECHNICAL FIELD

The present invention relates to a method of forming a resist patternwhich enables miniaturization of the pattern dimension and improvementin the uniformity of the pattern.

Priority is claimed on Japanese Patent Application No. 2011-130453,filed Jun. 10, 2011, the content of which is incorporated herein byreference.

BACKGROUND ART

In lithography techniques, for example, a resist film composed of aresist material is formed on a substrate, and the resist film issubjected to selective exposure of radial rays such as light or electronbeam through a mask having a predetermined pattern, followed bydevelopment, thereby forming a resist pattern having a predeterminedshape on the resist film.

A resist material in which the exposed portions become soluble in adeveloping solution is called a positive-type, and a resist material inwhich the exposed portions become insoluble in a developing solution iscalled a negative-type.

In recent years, in the production of semiconductor elements and liquidcrystal display elements, advances in lithography techniques have leadto rapid progress in the field of pattern miniaturization.

Typically, these miniaturization techniques involve shortening thewavelength (increasing the energy) of the exposure light source.Conventionally, ultraviolet radiation typified by g-line and i-lineradiation has been used, but nowadays KrF excimer lasers and ArF excimerlasers are starting to be introduced in mass production. Furthermore,research is also being conducted into lithography techniques that use anexposure light source having a wavelength shorter (energy higher) thanthese excimer lasers, such as electron beam, extreme ultravioletradiation (EUV), and X ray.

Resist materials for use with these types of exposure light sourcesrequire lithography properties such as a high resolution capable ofreproducing patterns of minute dimensions, and a high level ofsensitivity to these types of exposure light sources.

As a resist material that satisfies these conditions, a chemicallyamplified composition is used, which includes a base material componentthat exhibits a changed solubility in a developing solution under theaction of acid and an acid-generator component that generates acid uponexposure.

For example, in the case where the developing solution is an alkalideveloping solution (alkali developing process), a chemically amplifiedpositive resist which contains, as a base component (base resin), aresin which exhibits increased solubility in an alkali developingsolution under action of acid, and an acid generator is typically used.If the resist film formed using the resist composition is selectivelyexposed during formation of a resist pattern, then within the exposedportions, acid is generated from the acid-generator component, and theaction of this acid causes an increase in the solubility of the resincomponent in an alkali developing solution, making the exposed portionssoluble in the alkali developing solution. In this manner, the unexposedportions remain to form a positive resist pattern. The base resin usedexhibits increased polarity by the action of acid, thereby exhibitingincreased solubility in an alkali developing solution, whereas thesolubility in an organic solvent is decreased. Therefore, when such abase resin is applied to a process using a developing solutioncontaining an organic solvent (organic developing solution) (hereafter,this process is referred to as “solvent developing process” or “negativetone-developing process”) instead of an alkali developing process, thesolubility of the exposed portions in an organic developing solution isdecreased. As a result, in the solvent developing process, the unexposedportions of the resist film are dissolved and removed by the organicdeveloping solution, and a negative resist pattern in which the exposedportions are remaining is formed.

However, in the case of positive tone development process in which aresist composition that forms a positive resist pattern by an alkalidevelopment process, when a trench pattern (isolated space pattern) or ahole pattern is formed, it becomes necessary to form a resist patternusing an incident light weaker than that used in the case of a linepattern or a dot pattern, such that the contrast of the intensity of theincident light between exposed portions and unexposed portions becomesunsatisfactory. Therefore, pattern formation performance such asresolution tends to be restricted, and it becomes difficult to form aresist pattern with a high resolution.

In contrast, a negative tone development process using a negative type,chemically amplified resist composition (i.e., a chemically amplifiedresist composition which exhibits decreased alkali solubility in analkali developing solution upon exposure) in combination with an organicdeveloping solution is advantageous over the positive tone developmentprocess in the formation of a trench pattern or a hole pattern. For thisreason, in recent years, negative tone development process has beenconsidered important for formation of fine patterns, and base resins andthe like suitable for negative tone development process have beenproposed.

For example, Patent Document 1 discloses a negative-tone developmentresist composition containing a resin having a structural unit derivedfrom (meth)acrylate ester as a main chain, and a method of forming apattern.

As miniaturization of resist pattern is required, there has beenproposed methods in which a resist pattern is subjected to a thermaltreatment to fluidize the pattern and downsize the pattern (see PatentDocuments 2 to 4). For example, Patent Document 2 discloses a method inwhich a resist pattern is formed on a substrate, followed by a thermaltreatment to change the cross-sectional shape of the resist pattern froma rectangular shape to a semicircular shape to increase the bottomlength, thereby forming a minute pattern. Patent Document 3 discloses amethod in which a resist pattern is formed, followed by heating thepattern around its softening temperature, so as to fluidize the resistto change the pattern size, thereby forming a minute pattern. PatentDocument 4 discloses a method in which a positive resist compositioncontaining a resin having a specific structure is used to form a resistpattern, followed by a thermal flow treatment, thereby forming a minuteresist pattern.

DOCUMENTS OF RELATED ART Patent Document

-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2009-025723-   [Patent Document 2] Japanese Unexamined Patent Application, First    Publication No. Hei 1-307228-   [Patent Document 3] Japanese Unexamined Patent Application, First    Publication No. Hei 4-364021-   [Patent Document 4] Japanese Patent No. 4657883

SUMMARY OF THE INVENTION

Hereafter, as integration and miniaturization of semiconductor devicesfurther proceed, a method of forming a resist pattern capable of forminga more minute pattern is demanded. Further, it is required that theresist pattern is not only minute, but also the uniformity of thepattern be improved.

However, in a negative tone development, when a thermal treatment asdisclosed in Patent Documents 2 to 4 is conducted to downsize thepattern, i.e., reducing the intervals between the patterns (e.g., thediameter of hole in a contact hole pattern, the space width in the caseof a space (trench) pattern), there was a problem that the intervalsbetween the patterns are rather increased, so that the miniaturizationof the pattern cannot be achieved. In a negative tone development, aportion where part of groups are eliminated by exposure so as to exhibitdecreased solubility in a developing solution becomes a pattern portion(portion which becomes the side wall of a contact hole pattern or aspace pattern). It is presumed that, by conducting a thermal treatmentto such a pattern, gaps generated by elimination of groups by exposureare intruded by the film surrounding the gaps, so that the entire resistfilm and the pattern portions shrink, thereby resulting in the increaseof the intervals between the patterns. As such, in a negative tonedevelopment, there has been demanded a method in which pattern size canbe miniaturized simply without affecting the pattern portions, andimproving the pattern uniformity.

The present invention takes the above circumstances into consideration,with an object of providing a method of forming a resist pattern by anegative tone process using a developing solution containing an organicsolvent which enables miniaturization of the pattern size andimprovement in the pattern uniformity.

For solving the above-mentioned problems, the present invention employsthe following aspects.

Specifically, a first aspect of the present invention is a method offorming a resist pattern, including: a step of forming a resist film ona substrate using a resist composition containing a base component (A)which exhibits decreased solubility in an organic solvent under actionof acid and an acid-generator component (B) which generates acid uponexposure; a step of subjecting the resist film to exposure; a step ofpatterning the resist film by a negative-tone development using adeveloping solution containing the organic solvent to form a resistpattern; a step of applying a coating material to the resist pattern,thereby forming a coating film; a step of performing a thermal treatmentat a temperature lower than the softening point of the resist pattern,thereby heat shrinking the coating film to narrow an intervals betweenthe resist pattern; and a step of removing the coating film.

In the present description and claims, the term “aliphatic” is arelative concept used in relation to the term “aromatic”, and defines agroup or compound that has no aromaticity.

The term “alkyl group” includes linear, branched or cyclic, monovalentsaturated hydrocarbon, unless otherwise specified. The same applies forthe alkyl group within an alkoxy group.

The term “alkylene group” includes linear, branched or cyclic, divalentsaturated hydrocarbon, unless otherwise specified.

A “halogenated alkyl group” is a group in which part or all of thehydrogen atoms of an alkyl group is substituted with a halogen atom.Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

A “fluorinated alkyl group” or a “fluorinated alkylene group” is a groupin which part or all of the hydrogen atoms of an alkyl group or analkylene group have been substituted with fluorine atom(s).

The term “structural unit” refers to a monomer unit that contributes tothe formation of a polymeric compound (resin, polymer, copolymer).

An “acrylate ester” refers to a compound in which the terminal hydrogenatom of the carboxy group of acrylic acid (CH₂═CH—COOH) has beensubstituted with an organic group.

A “structural unit derived from an acrylate ester” refers to astructural unit that is formed by the cleavage of the ethylenic doublebond of an acrylate ester.

Examples of the substituent bonded to the carbon atom on the α-positionin the “acrylate ester which may have the hydrogen atom bonded to thecarbon atom on the α-position substituted with a substituent” include ahalogen atom, an alkyl group of 1 to 5 carbon atoms, a halogenated alkylgroup of 1 to 5 carbon atoms and a hydroxyalkyl group. With respect tothe “structural unit derived from an acrylate ester”, the “α-position(the carbon atom on the α-position)” refers to the carbon atom havingthe carbonyl group bonded thereto, unless specified otherwise.

Examples of the halogen atom as the substituent which may be bonded tothe carbon atom on the α-position include a fluorine atom, a chlorineatom, a bromine atom and an iodine atom.

Specific examples of the alkyl group of 1 to 5 carbon atoms for thesubstituent which may be bonded to the carbon atom on the α-positioninclude linear or branched alkyl groups such as a methyl group, an ethylgroup, a propyl group, an isopropyl group, an n-butyl group, an isobutylgroup, a tert-butyl group, a pentyl group, an isopentyl group and aneopentyl group.

Specific examples of the halogenated alkyl group of 1 to 5 carbon atomsfor the substituent include groups in which part or all of the hydrogenatoms of the aforementioned “alkyl group of 1 to 5 carbon atoms for thesubstituent” are substituted with halogen atoms. Examples of the halogenatom include a fluorine atom, a chlorine atom, a bromine atom and aniodine atom, and a fluorine atom is particularly desirable.

Specific examples of the hydroxyalkyl group of 1 to 5 carbon atoms forthe substituent include groups in which part or all of the hydrogenatoms of the aforementioned “alkyl group of 1 to 5 carbon atoms for thesubstituent” are substituted with hydroxy groups.

In the present invention, it is preferable that a hydrogen atom, analkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to5 carbon atoms is bonded to the carbon atom on the α-position, ahydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinatedalkyl group of 1 to 5 carbon atoms is more preferable, and in terms ofindustrial availability, a hydrogen atom or a methyl group is the mostdesirable.

The term “exposure” is used as a general concept that includesirradiation with any form of radiation.

According to the present invention, there is provided a method offorming a resist pattern by a negative tone process using a developingsolution containing an organic solvent which enables miniaturization ofthe pattern size and improvement in the pattern uniformity.

MODE FOR CARRYING OUT THE INVENTION

A method of forming a resist pattern according to a first aspect of thepresent invention includes: a step of forming a resist film on asubstrate using a resist composition containing a base component (A)which exhibits decreased solubility in an organic solvent under actionof acid and an acid-generator component (B) which generates acid uponexposure; a step of subjecting the resist film to exposure; a step ofpatterning the resist film by a negative-tone development using adeveloping solution containing the organic solvent to form a resistpattern; a step of applying a coating material to the resist pattern,thereby forming a coating film; a step of performing a thermal treatmentat a temperature lower than the softening point of the resist pattern,thereby heat shrinking the coating film to narrow an interval betweenthe resist pattern; and a step of removing the coating film.

In a negative tone-development resist composition used in the method offorming a resist pattern according to the present invention, when radialrays are irradiated (when exposure is conducted), acid is generated fromthe acid-generator component (B), and the solubility of the basecomponent (A) in an organic solvent is decreased by the action of theacid. Therefore, in the formation of a resist pattern, by conductingselective exposure of a resist film formed by using the negativetone-development resist composition, the solubility of the exposedportions in an organic developing solution containing an organicdeveloping solution is decreased, whereas the solubility of theunexposed portions in an organic developing solution is unchanged, andhence, a resist pattern can be formed by removing the unexposed portionsby negative tone development using an organic developing solution.

The negative tone-development resist composition used in the presentinvention will be described later in detail.

Hereinbelow, the method of forming a resist pattern according to thepresent invention will be specifically described referring to each ofthe steps.

Method of Forming Resist Pattern

(I) Resist Film Forming Step

Firstly, a negative tone-development resist composition is applied to asubstrate using a spinner or the like, and a bake treatment (postapplied bake (PAB)) is conducted at a temperature of 80 to 150° C. for40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film.

The substrate is not specifically limited and a conventionally knownsubstrate can be used. For example, substrates for electroniccomponents, and such substrates having wiring patterns formed thereoncan be used. Specific examples of the material of the substrate includemetals such as silicon wafer, copper, chromium, iron and aluminum; andglass. Suitable materials for the wiring pattern include copper,aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substratesprovided with an inorganic and/or organic film on the surface thereofmay be used. As the inorganic film, an inorganic antireflection film(inorganic BARC) can be used. As the organic film, an organicantireflection film (organic BARC) and an organic film such as alower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is method in which at least one layerof an organic film (lower-layer organic film) and at least one layer ofa resist film (upper resist film) are provided on a substrate, and aresist pattern formed on the upper resist film is used as a mask toconduct patterning of the lower-layer organic film. This method isconsidered as being capable of forming a pattern with a high aspectratio. More specifically, in the multilayer resist method, a desiredthickness can be ensured by the lower-layer organic film, and as aresult, the thickness of the resist film can be reduced, and anextremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method inwhich a double-layer structure consisting of an upper-layer resist filmand a lower-layer organic film is formed (double-layer resist method),and a method in which a multilayer structure having at least threelayers consisting of an upper-layer resist film, a lower-layer organicfilm and at least one intermediate layer (thin metal film or the like)provided between the upper-layer resist film and the lower-layer organicfilm (triple-layer resist method).

(II) Resist Film Exposure Step

Subsequently, the thus formed resist film is subjected to selectiveexposure, either by exposure through a mask having a predeterminedpattern formed thereon (mask pattern) using an exposure apparatus suchas an ArF exposure apparatus, an electron beam lithography apparatus oran EUV exposure apparatus, or by patterning via direct irradiation withan electron beam without using a mask pattern.

Following exposure, baking treatment (post exposure baking (PEB)) ispreferably conducted under temperature conditions of 80 to 150° C. for40 to 120 seconds, and preferably 60 to 90 seconds, so as tosatisfactorily proceed the deprotection reaction by the acid generatedupon exposure.

The wavelength to be used for exposure is not particularly limited andthe exposure can be conducted using radiation such as ArF excimer laser,KrF excimer laser, F₂ excimer laser, extreme ultraviolet rays (EUV),vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and softX-rays. The resist composition which can be used in the presentinvention (described later) is effective to KrF excimer laser, ArFexcimer laser, EB and EUV, and particularly effective to ArF excimerlaser, EB and EUV.

The exposure of the resist film can be either a general exposure (dryexposure) conducted in air or an inert gas such as nitrogen, orimmersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and thelens at the lowermost point of the exposure apparatus is pre-filled witha solvent (immersion medium) that has a larger refractive index than therefractive index of air, and the exposure (immersion exposure) isconducted in this state.

The immersion medium preferably exhibits a refractive index larger thanthe refractive index of air but smaller than the refractive index of theresist film to be exposed. The refractive index of the immersion mediumis not particularly limited as long at it satisfies the above-mentionedrequirements.

Examples of this immersion medium which exhibits a refractive index thatis larger than the refractive index of air but smaller than therefractive index of the resist film include water, fluorine-based inertliquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquidscontaining a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃,C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling pointwithin a range from 70 to 180° C. and preferably from 80 to 160° C. Afluorine-based inert liquid having a boiling point within theabove-mentioned range is advantageous in that the removal of theimmersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which allof the hydrogen atoms of the alkyl group are substituted with fluorineatoms is particularly desirable. Examples of these perfluoroalkylcompounds include perfluoroalkylether compounds and perfluoroalkylaminecompounds.

Specifically, one example of a suitable perfluoroalkylether compound isperfluoro(2-butyl-tetrahydrofuran) (boiling point 102° C.), and anexample of a suitable perfluoroalkylamine compound isperfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety,environment and versatility.

(III) Resist Pattern Forming Step

Next, the resist film after exposure is subjected to developingtreatment using a developing solution containing an organic solvent (anorganic developing solution), preferably followed by rinsing with arinse liquid containing an organic solvent, and then drying isconducted. By performing a rinse treatment, an excellent pattern can beformed.

After the developing treatment or the rinsing, the developing solutionor the rinse liquid remaining on the pattern can be removed by atreatment using a supercritical fluid.

If necessary, after the developing treatment, the rinsing or thetreatment with a supercritical fluid, a bake treatment (post bake) maybe conducted to remove any remaining organic solvent.

(Organic Developing Solution)

As the organic solvent contained in the organic developing solution usedfor developing, any of the conventional organic solvents can be usedwhich are capable of dissolving the base component (A) (prior toexposure) can be appropriately selected. Specific examples of theorganic solvent include polar solvents such as ketone solvents, estersolvents, alcohol solvents, amide solvents and ether solvents, andhydrocarbon solvents. Among these, ester solvents and ketone solventsare preferable. As an ester solvent, butyl acetate is preferable. As aketone solvent, methyl amyl ketone (2-heptanone) is preferable.

A ketone solvent is an organic solvent containing C—C(═O)—C within thestructure thereof. An ester solvent is an organic solvent containingC—C(═O)—O—C within the structure thereof. An alcohol solvent is anorganic solvent containing an alcoholic hydroxy group within thestructure thereof, and an “alcoholic hydroxy group” refers to a hydroxygroup bonded to a carbon atom of an aliphatic hydrocarbon group. Anamide solvent is an organic solvent containing an amide group within thestructure thereof. An ether solvent is an organic solvent containingC—O—C within the structure thereof. Some organic solvents have aplurality of the functional groups which characterizes theaforementioned solvents within the structure thereof. In such a case,the organic solvent can be classified as any type of the solvent havingthe characteristic functional group. For example, diethyleneglycolmonomethylether can be classified as either an alcohol solvent or anether solvent. A hydrocarbon solvent consists of a hydrocarbon, and doesnot have any substituent (atom or group other than hydrogen and carbon).

Examples of ketone solvents include 1-octanone, 2-octanone, 1-nonanone,2-nonanone, acetone, 4-heptanone, 1-hexanone, 2-hexanone, diisobutylketone, cyclohexanone, methylcyclohexanone, phenylacetone, methyl ethylketone, methyl isobutyl ketone, acetylacetone, acetonylacetone, ionone,diacetonylalcohol, acetylcarbinol, acetophenone, methyl naphthyl ketone,isophorone, propylenecarbonate, γ-butyrolactone and methyl amyl ketone(2-heptanone).

Examples of ester solvents include methyl acetate, butyl acetate, ethylacetate, isopropyl acetate, amyl acetate, isoamyl acetate, ethylmethoxyacetate, ehtyl ethoxyacetate, propylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, ethylene glycolmonopropyl ether acetate, ethylene glycol monobutyl ether acetate,ethylene glycol monophenyl ether acetate, diethylene glycol monomethylether acetate, diethylene glycol monopropyl ether acetate, diethyleneglycol monoethyl ether acetate, diethylene glycol monophenyl etheracetate, diethylene glycol monobutyl ether acetate, diethylene glycolmonoethyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate,4-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate,3-ethyl-3-methoxybutyl acetate, propylene glycol monomethyl etheracetate, propylene glycol monoethyl ether acetate, propylene glycolmonopropyl ether acetate, 2-ethoxybutyl acetate, 4-ethoxybutyl acetate,4-propoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentylacetate, 4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate,3-methyl-3-methoxypentyl acetate, 3-methyl-4-methoxypentyl acetate,4-methyl-4-methoxypentyl acetate, propylene glycol diacetate, methylformate, ethyl formate, butyl formate, propyl formate, ethyl lactate,butyl lactate, propyl lactate, ethyl carbonate, propyl carbonate, butylcarbonate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, butylpyruvate, methyl acetoacetate, ethyl acetoacetate, methyl propionate,ethyl propionate, propyl propionate, isopropyl propionate, methyl2-hydroxypropionate, ethyl 2-hydroxypropionate,methyl-3-methoxypropionate, ethyl-3-methoxypropionate,ethyl-3-ethoxypropionate and propyl-3-methoxypropionate.

As the ester solvent, a solvent represented by general formula (1)described later or a solvent represented by general formula (2)described later is preferable, a solvent represented by general formula(1) is more preferable, an alkyl acetate is still more preferable, andbutyl acetate is particularly desirable.

Examples of alcohol solvents include monohydric alcohols, such as methylalcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butylalcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol,n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, n-decanol and3-methoxy-1-butanol; glycol solvents, such as ethylene glycol,diethylene glycol and triethylene glycol; and glycol ether solventscontaining a hydroxy group, such as ethylene glycol monomethyl ether,propylene glycol monomethyl ether, diethylene glycol monomethyl ether,triethylene glycol monoethyl ether, methoxymethyl butanol, ethyleneglycol monoethyl ether, ethylene glycol monopropyl ether, ethyleneglycol monobutyl ether, propylene glycol monoethyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether and propyleneglycol monophenyl ether. Among these examples, a glycol ether solvent ispreferable.

Examples of amide solvents include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, hexamethylphosphoric amide and1,3-dimethyl-2-imidazolidinone.

Examples of ether solvents include the aforementioned glycol ethersolvents containing a hydroxy group; glycol ether solvents containing nohydroxy group, such as propylene glycol dimethyl ether, propylene glycoldiethyl ether, diethylene glycol dimethyl ether and diethylene glycoldiethyl ether: dioxane; tetrahydrofuran; anisole;perfluoro-2-butyltetrahydrofuran, perfluorotetrahydrofuran and1,4-dioxane. Among these, a glycol ether solvent containing a hydroxygroup or a glycol ether solvent containing no hydroxy group ispreferable.

Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents,such as pentane, hexane, octane, decane, 2,2,4-trimethylpentane,2,2,3-trimethylhexane, perfluorohexane and perfluoronpetane; andaromatic hydrocarbon solvents, such as toluene, xylene, ethylbenzene,propyl benzene, 1-methylpropylbenzene, 2-methylpropylbenzene,dimethylbenzene, diethylbenzene, ethylmethylbenzene, trimethylbenzene,ethyldimethylbenzene and dipropylbenzene. Among these examples, anaromatic hydrocarbon solvent is preferable.

These organic solvents can be used individually, or at least 2 solventsmay be mixed together. Further, an organic solvent other than theaforementioned examples or water may be mixed together.

As the organic solvent for the organic developing solution, a solventrepresented by general formula (1) or (2) shown below is preferable.R⁰⁰—C(═O)—O—R⁰¹  (1)R⁰²—C(═O)—O—R⁰³—O—R⁰⁴  (2)

In formula (1), each of R⁰⁰ and R⁰¹ independently represents a hydrogenatom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, acarboxy group, a hydroxy group, a cyano group or a halogen atom,provided that R⁰⁰ and R⁰¹ may be mutually bonded to form a ring. Informula (2), each of R⁰² and R⁰⁴ independently represents a hydrogenatom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, acarboxy group, a hydroxy group, a cyano group or a halogen atom,provided that R⁰² and R⁰⁴ may be mutually bonded to form a ring; and R⁰³represents an alkylene group.

In formula (1), the alkyl group for R⁰⁰ and R⁰¹ may be linear, branchedor cyclic, preferably linear or branched, and preferably has 1 to 5carbon atoms. The alkyl group may have a substituent. Examples of thesubstituent include a hydroxy group, a carboxy group and a cyano group.

As the alkyl group within the alkoxy group and the alkoxycarbonyl group,the same alkyl groups as those described above can be used.

Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom, and a fluorine atom is preferable.

It is preferable that R⁰⁰ and R⁰¹ each independently represents ahydrogen atom or an alkyl group.

Specific example of the solvent represented by formula (1) includemethyl acetate, butyl acetate, ethyl acetate, isopropyl acetate, pentylacetate, isopentyl acetate, methyl formate, ethyl formate, butylformate, propyl formate, ethyl lactate, butyl lactate, propyl lactate,ethyl carbonate, propyl carbonate, butyl carbonate, methyl pyruvate,ethyl pyruvate, propyl pyruvate, butyl pyruvate, methyl acetoacetate,ethyl acetoacetate, methyl propionate, ethyl propionate, propylpropionate, isopropyl propionate, methyl 2-hydroxypropionate and ethyl2-hydroxypropionate.

Among the aforementioned examples, as the solvent represented by formula(1), those in which R⁰⁰ and R⁰¹ both represent an unsubstituted alkylgroup is preferable, an alkyl acetate is more preferable, and butylacetate is particularly desirable.

In formula (2), R⁰² and R⁰⁴ are the same as defined for R⁰⁰ and R⁰¹described above.

The alkylene group for R⁰³ may be linear, branched or cyclic, preferablylinear or branched, and preferably has 1 to 5 carbon atoms. The alkylenegroup may have a substituent. Examples of the substituent include ahydroxy group, a carboxy group and a cyano group. When the alkylenegroup has 2 or more carbon atoms, an oxygen atom (—O—) may be presentbetween the carbon atoms within the alkylene group.

Specific example of the solvent represented by formula (2) includeethylene glycol monoethyl ether acetate, ethylene glycol monopropylether acetate, ethylene glycol monobutyl ether acetate, ethylene glycolmonophenyl ether acetate, diethylene glycol monomethyl ether acetate,diethylene glycol monopropyl ether acetate, diethylene glycol monophenylether acetate, diethylene glycol monobutyl ether acetate, diethyleneglycol monoethyl ether acetate, propylene glycol monomethyl etheracetate, propylene glycol monoethyl ether acetate, propylene glycolmonopropyl ether acetate, methyl-3-methoxypropionate,ethyl-3-methoxypropionate, ethyl-3-ethoxypropionate,propyl-3-methoxypropionate, ethyl methoxyacetate, ethyl ethoxyacetate,2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate,3-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate,2-ethoxybutyl acetate, 4-ethoxybutyl acetate, 4-propoxybutyl acetate,2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentylacetate, 2-methyl-3-methoxypentyl acetate, 3-methyl-3-methoxypentylacetate, 3-methyl-4-methoxypentyl acetate and 4-methyl-4-methoxypentylacetate.

The solvent represented by formula (1) and/or (2) can be usedindividually, or at least 2 types of solvents may be mixed together.Further, another solvent may be mixed together.

The other solvent is not particularly limited as long as it can be mixedwith the solvent represented by formula (1) or (2) without beingseparated, and can be appropriately selected from the aforementionedester solvents, ketone solvents, alcohol solvents, amide solvents, ethersolvents and hydrocarbon solvents.

In terms of reducing the cost, it is preferable to use an organicsolvent containing no halogen atom as the organic developing solution.The amount of the organic solvent containing no halogen atom, based onthe total weight of the organic developing solvent is preferably 60% byweight or more, more preferably 80% by weight or more, still morepreferably 90% by weight or more, and may be even 100% by weight.

The boiling point of the organic solvent used as the organic developingsolution is preferably 50° C. to lower than 250° C.

The ignition point of the organic solvent used as the organic developingsolution is preferably 200° C. or higher.

If desired, the organic developing solution may have a conventionaladditive blended. Examples of the additive include surfactants. Thesurfactant is not particularly limited, and for example, an ionic ornon-ionic fluorine and/or silicon surfactant can be used.

Examples of commercially available surfactants include fluorinesurfactants or silicon surfactants such as F Top EF301, EF303 (producedby Shinakita Kasei K.K.), Florad FC430, FC431 (produced by Sumitomo 3M),Megafac F171, F 173, F176, F189, R08 (produced by DIC Corporation),Surflon S-382, SC101, SC102, SC103, SC104, SC105, SC106 (Asahi GlassCompany, Limited) and Troysol S-366 (troy chemical corporation).Further, polysiloxane polymer KP-341 (produced by The Shin-etsu ChemicalIndustry Co., Ltd.) can be used as a silicon surfactant.

Further, other than the aforementioned conventional surfactants, therecan be used a surfactant containing a polymer having a fluoroaliphaticgroup derived from a fluoroaliphatic compound produced by atelomerization method (telomer method) or an oligomerization method(oligomer method). The fluoroaliphatic compound can be produced by amethod described in Japanese Unexamined Patent Application, FirstPublication No. 2002-90991.

As the polymer containing a fluoroaliphatic group, a copolymer of amonomer containing a fluoroaliphatic group and a(poly(oxyalkylene))acrylate and/or (poly(oxyalkylene))methacrylate ispreferable. The copolymer may be either a random copolymer or a blockcopolymer. Examples of the poly(oxyalkylene) group include apoly(oxyethylene group) a poly(oxypropylene) group and apoly(oxybutylene) group. Alternatively, a unit in which different typesof alkylene chains exist within the same chain may be used, such as apoly(block linkage of oxyethylene, oxypropylene and oxyethylene) or apoly(block linkage of oxyethylene and oxypropylene). Furthermore, thecopolymer of a monomer having a fluoroaliphatic group and a(poly(oxyalkylene))acrylate (or methacrylate) may not only be abipolymer, but may be a terpolymer or more in which 2 or more types ofmonomers having a fluoroaliphatic group or 2 or more types of(poly(oxyalkylene))acrylate (or methacrylate) have been copolymerizedtogether.

Examples of such surfactants which are commercially available includeMegafac F178, Megafac F470, Megafac F473, Megafac F475, Megafac F476 andMegafac F472 (produced by DIC Corporation). Further examples include acopolymer containing an acrylate (or a methacrylate) having a C6F13group and a (poly(oxyalkylene))acrylate (or methacrylate), a copolymercontaining an acrylate (or a methacrylate) having a C6F 13 group, a(poly(oxyethylene))acrylate (or methacrylate) and a(poly(oxypropylene))acrylate (or methacrylate), a copolymer containingan acrylate (or a methacrylate) having a C8F17 group and a(poly(oxyalkylene))acrylate (or methacrylate), and a copolymercontaining an acrylate (or a methacrylate) having a C₈F₁₇ group, a(poly(oxyethylene))acrylate (or methacrylate) and a(poly(oxypropylene))acrylate (or methacrylate).

As the surfactant, a non-ionic surfactant is preferable, and a fluorinesurfactant or a silicon surfactant is more preferable.

When a surfactant is added, the amount thereof based on the total amountof the organic developing solution is generally 0.001 to 5% by weight,preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% byweight.

The development treatment using the organic developing solution can beperformed by a conventional developing method. Examples thereof includea method in which the substrate is immersed in the developing solutionfor a predetermined time (a dip method), a method in which thedeveloping solution is cast up on the surface of the substrate bysurface tension and maintained for a predetermined period (a puddlemethod), a method in which the developing solution is sprayed onto thesurface of the substrate (spray method), and a method in which thedeveloping solution is continuously ejected from a developing solutionejecting nozzle while scanning at a constant rate to apply thedeveloping solution to the substrate while rotating the substrate at aconstant rate (dynamic dispense method).

(Rinse Liquid)

After the developing treatment and before drying, a rinse treatment maybe performed using a rinse liquid containing an organic solvent. Byperforming a rinse treatment, an excellent pattern can be formed.

As the organic solvent used for the rinse liquid, any of theaforementioned organic solvents for the organic developing solution canbe used which hardly dissolve the pattern. In general, at least onesolvent selected from the group consisting of hydrocarbon solvents,ketone solvents, ester solvents, alcohol solvents, amide solvents andether solvents is used. Among these, at least one solvent selected fromthe group consisting of hydrocarbon solvents, ketone solvents, estersolvents, alcohol solvents and amide solvents is preferable, morepreferably at least one solvent selected from the group consisting ofalcohol solvents and ester solvents, and an alcohol solvent isparticularly desirable.

The alcohol solvent used for the rinse liquid is preferably a monohydricalcohol of 6 to 8 carbon atoms, and the monohydric alcohol may belinear, branched or cyclic. Specific examples thereof include 1-hexanol,1-heptanol, 1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol,3-heptanol, 3-octanol, 4-octanol and benzyl alcohol. Among these,1-hexanol, 2-heptanol and 2-hexanol are preferable, and 1 hexanol and2-hexanol are more preferable.

These organic solvents can be used individually, or at least 2 solventsmay be mixed together. Further, an organic solvent other than theaforementioned examples or water may be mixed together. However, inconsideration of the development characteristics, the amount of waterwithin the rinse liquid, based on the total amount of the rinse liquidis preferably 30% by weight or less, more preferably 10% by weight orless, still more preferably 5% by weight or less, and most preferably 3%by weight or less.

If desired, the organic developing solution may have a conventionaladditive blended. Examples of the additive include surfactants. As thesurfactant, the same surfactants as those described above can bementioned, and a non-ionic surfactant is preferable, and a fluorinesurfactant or a silicon surfactant is more preferable.

When a surfactant is added, the amount thereof based on the total amountof the rinse liquid is generally 0.001 to 5% by weight, preferably 0.005to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The rinse treatment (washing treatment) using the rinse liquid can beperformed by a conventional rinse method. Examples thereof include amethod in which the rinse liquid is continuously applied to thesubstrate while rotating it at a constant rate (rotational coatingmethod), a method in which the substrate is immersed in the rinse liquidfor a predetermined time (dip method), and a method in which the rinseliquid is sprayed onto the surface of the substrate (spray method).

(IV) Coating Film Forming Step

Next, to the resist pattern obtained by the developing treatment, acoating material is applied by a spinner or the like, thereby forming acoating film of the coating material. The thickness of the coating filmis not particularly limited, but is preferably the same as or largerthan the height (thickness) of the pattern portion of the resist patternformed in the previous step. That is, it is preferable that the coatingfilm entirely cover the upper edge of the resist pattern.

After applying the coating material, the coating material may besubjected to drying under temperature conditions of 80 to 100° C. for 30to 90 seconds.

Further, after forming the coating film, a rinse treatment may beconducted, so as to remove excess coating material.

(Coating Material)

The coating material used in the present invention is not particularlylimited as long as it is capable of being coated on the resist patternand narrowing the intervals between the patterns. However, since thecoating material is applied to the pattern to form a film, it ispreferable that the coating material contains a component that dissolvesin water or an organic solvent at room temperature. Among these, thecoating material used in the present invention preferably contains acomponent that is capable of being dissolved in water at roomtemperature because an aqueous solvent hardly affects the resist patternwhich becomes a lower layer when the coating material is appliedthereto. It is particularly desirable that the coating material containsan aqueous polymer. Further, because the coating film will be removed ina later step, an aqueous polymer is preferable in terms of ease inremovability.

Specific examples of aqueous polymers include alkylene glycol polymers,cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers,epoxy polymers, melamine polymers and nylon polymers. The coatingmaterial used in the present invention preferably contains at least oneaqueous polymer selected from the group consisting of theabove-described aqueous polymers.

Examples of alkylene glycol polymers include polymers or copolymers(addition polymers or addition copolymers) containing alkylene glycolmonomers such as ethylene glycol and propylene glycol.

Examples of cellulosic derivatives include polymers and copolymerscontaining cellulose monomers such as hydroxypropyl methylcellulosephthalate, hydroxypropyl cellulose acetate phthalate, hydroxypropylmethylcellulose hexahydrophthalate, hydroxypropyl methylcelluloseacetate succinate, hydroxypropyl methyl cellulose, hydroxypropylcellulose, hydroxyethyl cellulose, cellulose acetate hexahydrophthalate,carboxymethyl cellulose, ethyl cellulose and methyl cellulose.

Examples of vinyl polymers include polymers and copolymers containingvinyl monomers such as N-vinyl pyrrolidone, vinyl imidazolidinone andvinyl acetate.

Examples of acrylic polymers include polymers and copolymers containingacrylic monomers such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethyl acrylamide,N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropylacrylamide, N-methyl acrylamide, diacetone acrylamide,N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate,N,N-dimethylaminoethyl acrylate and acryloylmorpholine.

Examples of urea polymers include polymers and copolymers containingurea monomers such as methylol urea, dimethylol urea and ethylene urea.

As the epoxy polymer, there is no particular limitation as long as it isan epoxy polymer which is soluble in water, and examples thereof includediethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, glycerol polyglycidyl ether and polyglycerol polyglycidyl ether.

Examples of melamine polymers include melamine polymers having as acomponent thereof methoxymethyl melamine, isobutoxymethyl methoxymethylmelamine and methoxyethyl melamine.

As the nylon polymer, there is no particular limitation as long as it isa nylon polymer which is soluble in water, and can be obtained by ahydrophilic monomer such as acrylic acid to nylon.

The coating material used in the present invention preferably containsat least one member selected from the group consisting of alkyleneglycol polymers, cellulose polymers, vinyl polymers and acrylicpolymers, and it is particularly desirable that the coating materialcontains an acrylic polymer. By using an acrylic polymer, due to theacidic pH of the acrylic polymer, it becomes easier to adjust the pH ofthe coating material by appropriately combining with other components(described later) which can be contained in the coating material.Further, by using an acrylic polymer, when heating is conducted in thethermal treatment step described later, the coating film of the coatingmaterial does not cause reactions such as cross-linking with the resistpattern, so that the coating film can be easily removed.

As the acrylic polymer, an acrylic polymer consisting of acrylatemonomers may be used, although a copolymer with other monomers ispreferable in that the size of the resist pattern can be narrowed. Asthe other monomer, an N-vinylpyrrolidone monomer is preferably becausethe shrink ratio at the time of heating is particularly large. When anN-vinylpyrrolidone monomer is used, the N-vinylpyrrolidone monomerfunctions as a proton doner, and the acrylic monomer functions as aproton acceptor.

When the aqueous polymer is used as a copolymer, the compositional ratiois not particularly limited. However, when the stability with time isconsidered as an important factor, it is preferable that the blend ratioof the acrylic polymer be larger than the other polymer components.Other than blending excess amount of acrylic polymer as described above,the stability with time can be improved by adding an acidic compoundsuch as p-toluenesulfonic acid or dodecylbenzenesulfonic acid.

As the aqueous polymer, one type of polymer may be used alone, or two ormore types of polymers may be used in combination.

The coating material may further contain an aqueous amine. By blendingan aqueous amine, generation of impurities can be prevented, and pH canbe easily adjusted.

As the aqueous amine, in terms of preventing generation of impuritiesand adjusting pH, among the amines described later for the (D) componentof the resist composition, amines exhibiting pKa (acid dissociationconstant) in an aqueous solution at 25° C. of 7.5 to 13 are preferable,aliphatic amines are more preferable, and triethylamine is particularlydesirable.

In the present invention, when the coating material contains an aqueousamine, the amount of the aqueous amine based on the total solid contentof the coating material is preferably 0.1 to 30% by weight, and morepreferably 2 to 15% by weight. When the amount of the aqueous amine isat least as large as the lower limit of the above-mentioned range,deterioration of the coating material with time can be prevented. On theother hand, when the amount of the aqueous amine is no more than theupper limit of the above-mentioned range, the resist pattern whichbecomes a lower layer is not adversely affected.

Furthermore, the coating material preferably contains a surfactant. Byusing a surfactant, generation of defects can be effectively prevented.The surfactant is not particularly limited, and any surfactant typicallyused for resist compositions can be used. Examples of particularlypreferable surfactants include N-alkylpyrrolidone surfactants,quaternary ammonium salt surfactants and polyoxyethylene phosphatesurfactants.

In the present invention, the coating material is preferably dissolvedin water or a mixed solvent of water and an alcohol solvent (the alcoholcontent preferably being 30% by weight or less) for use. As examples ofthe alcohol solvent, the same alcohol solvents as those described abovefor the developing solution can be given. The solid content within thecoating material is preferably 3 to 50% by weight, and more preferably 5to 20% by weight.

Further, from the viewpoint of miniaturization of pattern size,suppressing generation of defects, and the like, if desired, a non-aminewater-soluble organic solvent may be added.

In the present invention, the pH of the coating material used is notparticularly limited, but in consideration of hardly affecting theresist pattern as a lower layer, the pH is preferably 11 or less, morepreferably 1 to 9, still more preferably 1 to 7, and most preferably 1to 5.

(V) Thermal Treatment Step

The resist pattern and the coating film formed on the substrate asdescribed above is subjected to a thermal treatment at a temperaturelower than the softening point of the resist pattern. Here, thesoftening point of the resist pattern refers to a bake treatmenttemperature at which heat fluid flow of the pattern occurs and change inthe size starts when a resist pattern formed on a substrate is subjectedto baking.

By conducting thermal treatment, heat shrinking of the coating filmcovering the resist pattern occurs. As a result, side walls of thepattern portions of the resist pattern (i.e., portions where the resistfilm remain) is pulled toward the space portions of a space pattern(trench pattern) or hole portions of a contact hole pattern (i.e.,portions where the resist film has been removed), so that the intervalsbetween the resist patterns become narrower than those prior to the heatshrinking.

The heating temperature is not particularly limited, as long as it is atemperature which causes heat shrinking of the coating film and does notcause softening of the resist pattern (i.e., a temperature lower thanthe softening point of the resist pattern), and the heating temperaturecan be appropriately selected depending on the types of the coatingmaterial and the resist composition. When a general coating material anda general resist composition are used, the heating temperature is about80 to 200° C.

(VI) Coating Film Removing Step

Finally, the coating film which has been subjected to the thermaltreatment is removed.

The method of removing the coating film is not particularly limited, andcan be appropriately selected depending on the type of the coatingmaterial. For example, when the coating material is an aqueous polymerdissolved in water or a mixed solvent of water and an alcohol solvent,washing can be conducted for 10 to 120 seconds using an aqueous solvent,preferably pure water, thereby removing the coating film. The washingtreatment can be conducted in the same manner as in the rinse treatmentusing the aforementioned rinse liquid.

In the present invention, by removing the coating film after narrowingthe intervals between the patterns, the coating film would not affectthe shape of the resist pattern (cause generation of size defect), andbecome an obstacle in a later step such as etching.

Negative Tone-Development Resist Composition

The negative tone-development resist composition used in the method offorming a resist pattern according to the present invention (hereafter,frequently referred to simply as “resist composition”) includes a basecomponent (A) (hereafter, referred to as “component (A)”) which exhibitsdecreased solubility in an organic developing solution under action ofacid and an acid-generator component (B) (hereafter, referred to as“component (B)”) which generates acid upon irradiation, and is used inthe method of forming a resist pattern described above.

In the resist composition, when radial rays are irradiated (whenexposure is conducted), at exposed portions, acid is generated from thecomponent (B), and the solubility of the component (A) in an organic isdecreased by the action of the generated acid. Therefore, in theformation of a resist pattern, by conducting selective exposure of aresist film formed by using the resist composition, the solubility ofthe exposed portions in a developing solution containing an organicdeveloping solution is decreased, whereas the solubility of theunexposed portions in an organic developing solution is unchanged, andhence, a resist pattern can be formed by removing the unexposed portionsby negative tone development using an organic developing solution.

<Component (A)>

As the component (A), an organic compound typically used as a basecomponent for a chemically amplified resist composition can be usedalone, or two or more of such organic compounds can be mixed together.

Here, the term “base component” refers to an organic compound capable offorming a film, and is preferably an organic compound having a molecularweight of 500 or more. When the organic compound has a molecular weightof 500 or more, the film-forming ability is improved, and a resistpattern of nano level can be easily formed.

The “organic compound having a molecular weight of 500 or more” whichcan be used as a base component is broadly classified into non-polymersand polymers.

In general, as a non-polymer, any of those which have a molecular weightin the range of 500 to less than 4,000 is used. Hereafter, a non-polymerhaving a molecular weight in the range of 500 to less than 4,000 isreferred to as a low molecular weight compound.

As a polymer, any of those which have a molecular weight of 1,000 ormore is generally used. Hereafter, a polymer having a molecular weightof 1,000 or more is referred to as a polymeric compound. With respect toa polymeric compound, the “molecular weight” is the weight averagemolecular weight in terms of the polystyrene equivalent value determinedby gel permeation chromatography (GPC). Hereafter, a polymeric compoundis frequently referred to simply as a “resin”.

As the component (A), a resin component which exhibits changedsolubility in a developing solution under action of acid may be used.Alternatively, as the component (A), a low molecular weight materialwhich exhibits changed solubility in a developing solution under actionof acid may be used.

Since the resist composition used in the present invention is a resistcomposition which forms a negative pattern in a solvent developingprocess, it is preferable to use a base component (A0) (hereafter,referred to as “component (A0)”) which exhibits increased polarity bythe action of acid. By using the component (A0), since the polarity ofthe base component changes prior to and after exposure, an excellentdevelopment contrast can be obtained in a solvent developing process.

The component (A0) exhibits high solubility in an organic developingsolution prior to exposure, and when acid is generated from thecomponent (B) upon exposure, the polarity of the component (A0) isincreased by the action of the generated acid, thereby decreasing thesolubility of the component (A0) in an organic developing solution.Therefore, in the formation of a resist pattern, by conducting selectiveexposure of a resist film formed by applying the resist composition to asubstrate, the exposed portions changes from an soluble state to aninsoluble state in an organic developing solution, whereas the unexposedportions remain soluble in an organic developing solution. As a result,by conducting development using an organic developing solution, acontrast can be made between the exposed portions and unexposedportions, thereby enabling the formation of a negative resist pattern.

The component (A0) may be a resin component (A1) that exhibits increasedpolarity under the action of acid (hereafter, frequently referred to as“component (A1)”), a low molecular weight material (A2) that exhibitsincreased polarity under the action of acid (hereafter, frequentlyreferred to as “component (A2)”), or a mixture thereof.

[Component (A1)]

As the component (A1), a resin component (base resin) typically used asa base component for a chemically amplified resist composition can beused alone, or two or more of such resin components can be mixedtogether.

In the present invention, the component (A1) preferably has a structuralunit derived from an acrylate ester which may have the hydrogen atombonded to the carbon atom on the α-position substituted with asubstituent.

In the resist composition used in the present invention, it isparticularly desirable that the component (A1) has a structural unit(a1) derived from an acrylate ester which may have the hydrogen atombonded to the carbon atom on the α-position substituted with asubstituent and contains an acid decomposable group which exhibitsincreased polarity by the action of acid.

The component (A1) preferably includes, in addition to the structuralunit (a1), at least one structural unit (a2) selected from the groupconsisting of a structural unit derived from an acrylate estercontaining an —SO₂— containing cyclic group and which may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent and a structural unit derived from an acrylate estercontaining a lactone-containing cyclic group and which may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent.

Furthermore, it is preferable that the component (A1) include astructural unit (a3) derived from an acrylate ester containing a polargroup-containing aliphatic hydrocarbon group and may have the hydrogenatom bonded to the carbon atom on the α-position substituted with asubstituent, as well as the structural unit (a1), or the structural unit(a1) and the structural unit (a2).

(Structural Unit (a1))

The structural unit (a1) is a structural unit derived from an acrylateester which may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an aciddecomposable group which exhibits increased polarity by the action ofacid.

The term “acid decomposable group” refers to a group in which at least apart of the bond within the structure thereof is cleaved by the actionof acid generated from the component (B) upon exposure.

Examples of acid decomposable groups which exhibit increased polarity bythe action of an acid include groups which are decomposed by the actionof an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, anamino group and a sulfo group (—SO₃H). Among these, a polar groupcontaining —OH in the structure thereof (hereafter, referred to as“OH-containing polar group”) is preferable, and a carboxy group or ahydroxy group is more preferable.

More specifically, as an example of an acid decomposable group, a groupin which the aforementioned polar group has been protected with an aciddissociable group (such as a group in which the hydrogen atom of theOH-containing polar group has been protected with an acid dissociablegroup) can be given.

An “acid dissociable group” is a group in which at least the bondbetween the acid dissociable group and the adjacent carbon atom iscleaved by the action of acid generated from the component (B) uponexposure. It is necessary that the acid dissociable group thatconstitutes the acid decomposable group is a group which exhibits alower polarity than the polar group generated by the dissociation of theacid dissociable group. Thus, when the acid dissociable group isdissociated by the action of acid, a polar group exhibiting a higherpolarity than that of the acid dissociable group is generated, therebyincreasing the polarity. As a result, the polarity of the entirecomponent (A1) is increased. By the increase in the polarity, in thecase of applying an alkali developing process, the solubility in analkali developing solution is relatively increased. On the other hand,in the case of applying a solvent developing process, the solubility inan organic developing solution containing an organic solvent decreases.

As the acid dissociable group for the structural unit (a1), any of thosewhich have been proposed as acid dissociable groups for a base resin ofa chemically amplified resist may be used. Generally, groups that formeither a cyclic or chain-like tertiary alkyl ester with the carboxylgroup of the (meth)acrylic acid, and acetal-type acid dissociable groupssuch as alkoxyalkyl groups are widely known.

Here, a tertiary alkyl ester describes a structure in which an ester isformed by substituting the hydrogen atom of a carboxyl group with achain-like or cyclic tertiary alkyl group, and a tertiary carbon atomwithin the chain-like or cyclic tertiary alkyl group is bonded to theoxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). Inthis tertiary alkyl ester, the action of acid causes cleavage of thebond between the oxygen atom and the tertiary carbon atom, therebyforming a carboxy group. As a result, the polarity of the component (A1)is increased.

The chain-like or cyclic alkyl group may have a substituent.

Hereafter, for the sake of simplicity, groups that exhibit aciddissociability as a result of the formation of a tertiary alkyl esterwith a carboxyl group are referred to as “tertiary alkyl ester-type aciddissociable groups”.

Examples of tertiary alkyl ester-type acid dissociable groups includealiphatic branched, acid dissociable groups and aliphatic cyclicgroup-containing acid dissociable groups.

In the present description and claims, the term “aliphatic branched”refers to a branched structure having no aromaticity.

The “aliphatic branched, acid dissociable group” is not limited to beconstituted of only carbon atoms and hydrogen atoms (not limited tohydrocarbon groups), but is preferably a hydrocarbon group.

Further, the “hydrocarbon group” may be either saturated or unsaturated,but is preferably saturated.

Examples of aliphatic branched, acid dissociable groups include tertiaryalkyl groups of 4 to 8 carbon atoms, and specific examples include atert-butyl group, tert-pentyl group and tert-heptyl group.

The term “aliphatic cyclic group” refers to a monocyclic group orpolycyclic group that has no aromaticity.

The “aliphatic cyclic group” within the structural unit (a1) may or maynot have a substituent. Examples of the substituent include an alkylgroup of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, afluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and anoxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituentsis not limited to be constituted from only carbon and hydrogen (notlimited to hydrocarbon groups), but is preferably a hydrocarbon group.Further, the “hydrocarbon group” may be either saturated or unsaturated,but is preferably saturated. Furthermore, the “aliphatic cyclic group”is preferably a polycyclic group.

As such aliphatic cyclic groups, groups in which one or more hydrogenatoms have been removed from a monocycloalkane or a polycycloalkane suchas a bicycloalkane, tricycloalkane or tetracycloalkane which may or maynot be substituted with an alkyl group of 1 to 5 carbon atoms, afluorine atom or a fluorinated alkyl group, may be used. Specificexamples include groups in which one or more hydrogen atoms have beenremoved from a monocycloalkane such as cyclopentane and cyclohexane; andgroups in which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

As the aliphatic cyclic group-containing acid dissociable group, forexample, a group which has a tertiary carbon atom on the ring structureof the cycloalkyl group can be used. Specific examples include groupsrepresented by any one of general formulas (1-1) to (1-9) shown below,such as a 2-methyl-2-adamantyl group and a 2-ethyl-2-adamantyl group.

Further, as examples of aliphatic branched acid dissociable group,groups having an aliphatic cyclic group such as an adamantyl group,cyclohexyl group, cyclopentyl group, norbornyl group, tricyclodecylgroup or tetracyclododecyl group, and a branched alkylene group having atertiary carbon atom bonded thereto, as those represented by generalformulas (2-1) to (2-6) shown below, can be given.

In the formulas above, R¹⁴ represents an alkyl group; and g representsan integer of 0 to 8.

In the formulas, each of R¹⁵ and R¹⁶ independently represents an alkylgroup (which may be linear or branched, and preferably has 1 to 5 carbonatoms).

As the alkyl group for R¹⁴, a linear or branched alkyl group ispreferable.

The linear alkyl group preferably has 1 to 5 carbon atoms, morepreferably 1 to 4, and still more preferably 1 or 2. Specific examplesinclude a methyl group, an ethyl group, an n-propyl group, an n-butylgroup and an n-pentyl group. Among these, a methyl group, an ethyl groupor an n-butyl group is preferable, and a methyl group or an ethyl groupis more preferable.

The branched alkyl group preferably has 3 to 10 carbon atoms, and morepreferably 3 to 5. Specific examples of such branched alkyl groupsinclude an isopropyl group, an isobutyl group, a tert-butyl group, anisopentyl group and a neopentyl group, and an isopropyl group or atert-butyl group is particularly desirable.

g is preferably an integer of 0 to 3, more preferably 1 to 3, and stillmore preferably 1 or 2.

As the alkyl group for R¹⁵ and R¹⁶, the same alkyl groups as those forR¹⁴ can be used.

In formulas (1-1) to (1-9) and (2-1) to (2-6), part of the carbon atomsconstituting the ring may be replaced with an ethereal oxygen atom(—O—).

Further, in formulas (1-1) to (1-9) and (2-1) to (2-6), one or more ofthe hydrogen atoms bonded to the carbon atoms constituting the ring maybe substituted with a substituent. Examples of the substituent includean alkyl group of 1 to 5 carbon atoms, a fluorine atom and a fluorinatedalkyl group.

An “acetal-type acid dissociable group” generally substitutes a hydrogenatom at the terminal of an OH-containing polar group such as a carboxygroup or hydroxyl group, so as to be bonded with an oxygen atom. Whenacid is generated upon exposure, the generated acid acts to break thebond between the acetal-type acid dissociable group and the oxygen atomto which the acetal-type, acid dissociable group is bonded, therebyforming an OH-containing polar group such as a carboxy group or ahydroxy group. As a result, the polarity of the component (A1) isincreased.

Examples of acetal-type acid dissociable groups include groupsrepresented by general formula (p1) shown below.

In the formula, each of R¹′ and R²′ independently represent a hydrogenatom or an alkyl group of 1 to 5 carbon atoms; n represents an integerof 0 to 3; and Y²¹ represents an alkyl group of 1 to 5 carbon atoms oran aliphatic cyclic group.

In general formula (p1) above, n is preferably an integer of 0 to 2,more preferably 0 or 1, and most preferably 0.

As the alkyl group of 1 to 5 carbon atoms for R¹′ and R²′, the samealkyl groups of 1 to 5 carbon atoms as those described above for R canbe used, although a methyl group or ethyl group is preferable, and amethyl group is particularly desirable.

In the present invention, it is preferable that at least one of R¹′ andR²′ be a hydrogen atom. That is, it is preferable that the aciddissociable group (p1) is a group represented by general formula (p1-1)shown below.

In the formula, R¹′, n and Y²¹ are the same as defined above.

As the alkyl group of 1 to 5 carbon atoms for Y²¹, the same alkyl groupsof 1 to 5 carbon atoms as those described above can be used.

As the aliphatic cyclic group for Y²¹, any of the aliphaticmonocyclic/polycyclic groups which have been proposed for conventionalArF resists and the like can be appropriately selected for use. Forexample, the same groups described above in connection with the“aliphatic cyclic group” can be used.

Further, as the acetal-type, acid dissociable group, groups representedby general formula (p2) shown below can also be used.

In the formula, R¹⁷ and R¹⁸ each independently represent a linear orbranched alkyl group or a hydrogen atom; and R¹⁹ represents a linear,branched or cyclic alkyl group; or R¹⁷ and R¹⁹ each independentlyrepresents a linear or branched alkylene group, and the terminal of R¹⁷is bonded to the terminal of R¹⁹ to form a ring.

The alkyl group for R¹⁷ and R¹⁸ preferably has 1 to 15 carbon atoms, andmay be either linear or branched. As the alkyl group, an ethyl group ora methyl group is preferable, and a methyl group is most preferable. Itis particularly desirable that either one of R¹⁷ and R¹⁸ be a hydrogenatom, and the other be a methyl group.

R¹⁹ represents a linear, branched or cyclic alkyl group which preferablyhas 1 to 15 carbon atoms, and may be any of linear, branched or cyclic.

When R¹⁹ represents a linear or branched alkyl group, it is preferablyan alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group ormethyl group, and most preferably an ethyl group.

When R¹⁹ represents a cycloalkyl group, it preferably has 4 to 15 carbonatoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10carbon atoms. As examples of the cycloalkyl group, groups in which oneor more hydrogen atoms have been removed from a monocycloalkane or apolycycloalkane such as a bicycloalkane, tricycloalkane ortetracycloalkane, which may or may not be substituted with a fluorineatom or a fluorinated alkyl group, may be used. Examples of such groupsinclude groups in which one or more hydrogen atoms have been removedfrom a monocycloalkane such as cyclopentane or cyclohexane; and groupsin which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane. Among these, a group in which oneor more hydrogen atoms have been removed from adamantane is preferable.

In general formula (p2) above, R¹⁷ and R¹⁹ may each independentlyrepresent a linear or branched alkylene group (preferably an alkylenegroup of 1 to 5 carbon atoms), and the terminal of R¹⁹ may be bonded tothe terminal of R17.

In such a case, a cyclic group is formed by R¹⁷, R¹⁹, the oxygen atomhaving R¹⁹ bonded thereto, and the carbon atom having the oxygen atomand R¹⁷ bonded thereto. Such a cyclic group is preferably a 4- to7-membered ring, and more preferably a 4- to 6-membered ring. Specificexamples of the cyclic group include tetrahydropyranyl group andtetrahydrofuranyl group.

As the structural unit (a1), it is preferable to use at least one memberselected from the group consisting of structural units represented byformula (a1-0-1) shown below and structural units represented by formula(a1-0-2) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; and X¹represents an acid dissociable group.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X²represents an acid dissociable group; and Y²² represents a divalentlinking group.

In general formula (a1-0-1) above, the alkyl group of 1 to 5 carbonatoms or halogenated alkyl group of 1 to 5 carbon atoms for R are thesame as the alkyl group of 1 to 5 carbon atoms or halogenated alkylgroup of 1 to 5 carbon atoms which can be used as the substituent forthe hydrogen atom bonded to the carbon atom on the α-position of theaforementioned acrylate ester.

X¹ is not particularly limited as long as it is an acid dissociablegroup. Examples thereof include the aforementioned tertiary alkylester-type acid dissociable groups and acetal-type acid dissociablegroups, and tertiary alkyl ester-type acid dissociable groups arepreferable.

In general formula (a1-0-2), R is the same as defined above.

X² is the same as defined for X¹ in general formula (a1-0-1).

As preferable examples of the divalent linking group for Y²², a divalenthydrocarbon group which may have a substituent, and a divalent linkinggroup containing a hetero atom can be given.

A hydrocarbon “has a substituent” means that part or all of the hydrogenatoms within the hydrocarbon group is substituted with groups or atomsother than hydrogen.

The hydrocarbon group may be either an aliphatic hydrocarbon group or anaromatic hydrocarbon group. An “aliphatic hydrocarbon group” refers to ahydrocarbon group that has no aromaticity.

The aliphatic hydrocarbon group may be saturated or unsaturated. Ingeneral, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group for thehydrocarbon group as Y²², a linear or branched aliphatic hydrocarbongroup, and an aliphatic hydrocarbon group having a ring in the structurethereof can be given.

The linear or branched aliphatic hydrocarbon group preferably has 1 to10 carbon atoms, more preferably 1 to 8, still more preferably 1 to 5,and most preferably 1 or 2.

As the linear aliphatic hydrocarbon group, a linear alkylene group ispreferable. Specific examples thereof include a methylene group [—CH₂—],an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃—], atetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groupsare preferred, and specific examples include various alkylalkylenegroups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—,—C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂—;alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—,—C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylenegroups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; andalkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and—CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, alinear alkyl group of 1 to 5 carbon atoms is preferable.

The linear or branched aliphatic hydrocarbon group (chain-like aliphatichydrocarbon group) may or may not have a substituent. Examples of thesubstituent include a fluorine atom, a fluorinated alkyl group of 1 to 5carbon atoms, and an oxygen atom (═O).

As examples of the hydrocarbon group containing a ring in the structurethereof, a cyclic aliphatic hydrocarbon group (a group in which twohydrogen atoms have been removed from an aliphatic hydrocarbon ring),and a group in which the cyclic aliphatic hydrocarbon group is bonded tothe terminal of the aforementioned chain-like aliphatic hydrocarbongroup or interposed within the aforementioned chain-like aliphatichydrocarbon group, can be given.

The cyclic aliphatic hydrocarbon group preferably has 3 to 20 carbonatoms, and more preferably 3 to 12 carbon atoms.

The cyclic aliphatic hydrocarbon group may be either a polycyclic groupor a monocyclic group. As the monocyclic group, a group in which twohydrogen atoms have been removed from a monocycloalkane of 3 to 6 carbonatoms is preferable. Examples of the monocycloalkane includecyclopentane and cyclohexane.

As the polycyclic group, a group in which two hydrogen atoms have beenremoved from a polycycloalkane of 7 to 12 carbon atoms is preferable.Examples of the polycycloalkane include adamantane, norbornane,isobornane, tricyclodecane and tetracyclododecane.

The cyclic aliphatic hydrocarbon group may or may not have asubstituent. Examples of the substituent include an alkyl group of 1 to5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5carbon atoms, and an oxygen atom (═O).

Examples of the aforementioned aromatic hydrocarbon group for Y²²include a divalent aromatic hydrocarbon group in which one hydrogen atomhas been removed from a benzene ring of a monovalent aromatichydrocarbon group such as a phenyl group, a biphenyl group, a fluorenylgroup, a naphthyl group, an anthryl group or a phenanthryl group; anaromatic hydrocarbon group in which part of the carbon atomsconstituting the ring of the aforementioned divalent aromatichydrocarbon group has been substituted with a hetero atom such as anoxygen atom, a sulfur atom or a nitrogen atom; and an aromatichydrocarbon group in which one hydrogen atom has been removed from abenzene ring of an arylalkyl group such as a benzyl group, a phenethylgroup, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a1-naphthylethyl group or a 2-naphthylethyl group.

The aromatic hydrocarbon group may or may not have a substituent.Examples of the substituent include an alkyl group of 1 to 5 carbonatoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbonatoms, and an oxygen atom (═O).

When Y²² represents a divalent linking group containing a hetero atom,examples thereof include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—,—C(═O)—NH—, —NH—(H may be substituted with a substituent such as analkyl group or an acyl group), —S—, —S(═O)₂—, —S(═O)₂—O—, “-A-O—B—(wherein O is an oxygen atom, and each of A and B independentlyrepresents a divalent hydrocarbon group which may have a substituent)”and a combination of a divalent hydrocarbon group which may have asubstituent with a divalent linking group containing a hetero atom. Asexamples of the divalent hydrocarbon group which may have a substituent,the same groups as those described above for the hydrocarbon group whichmay have a substituent can be given, and a linear or branched aliphatichydrocarbon group or an aliphatic hydrocarbon group containing a ring inthe structure thereof is preferable.

When Y²² represents a divalent linking group —NH— and the H in theformula is replaced with a substituent such as an alkyl group or an acylgroup, the substituent preferably has 1 to 10 carbon atoms, morepreferably 1 to 8 carbon atoms, and most preferably 1 to 5 carbon atoms.

When Y²² is “A-O—B”, each of A and B independently represents a divalenthydrocarbon group which may have a substituent.

The hydrocarbon group for A may be either an aliphatic hydrocarbongroup, or an aromatic hydrocarbon group. An “aliphatic hydrocarbongroup” refers to a hydrocarbon group that has no aromaticity.

The aliphatic hydrocarbon group for A may be either saturated orunsaturated. In general, the aliphatic hydrocarbon group is preferablysaturated.

As specific examples of the aliphatic hydrocarbon group for A, a linearor branched aliphatic hydrocarbon group, and an aliphatic hydrocarbongroup having a ring in the structure thereof can be given. These are thesame as defined above.

Among these, as A, a linear aliphatic hydrocarbon group is preferable,more preferably a linear alkylene group, still more preferably a linearalkylene group of 2 to 5 carbon atoms, and most preferably an ethylenegroup.

As the hydrocarbon group for B, the same divalent hydrocarbon groups asthose described above for A can be used.

As B, a linear or branched aliphatic hydrocarbon group is preferable,and a methylene group or an alkylmethylene group is particularlydesirable.

The alkyl group within the alkyl methylene group is preferably a linearalkyl group of 1 to 5 carbon atoms, more preferably a linear alkyl groupof 1 to 3 carbon atoms, and most preferably a methyl group.

Specific examples of the structural unit (a1) include structural unitsrepresented by general formulas (a1-1) to (a1-4) shown below.

In the formulas, X′ represents a tertiary alkyl ester-type aciddissociable group; Y²¹ represents an alkyl group of 1 to 5 carbon atomsor an aliphatic cyclic group; n represents an integer of 0 to 3; Y²²represents a divalent linking group; R is the same as defined above; andeach of R¹′ and R²′ independently represents a hydrogen atom or an alkylgroup of 1 to 5 carbon atoms.

Examples of the tertiary alkyl ester-type acid dissociable group for X′include the same tertiary alkyl ester-type acid dissociable groups asthose described above for X¹.

R¹′, R²′, n and Y²¹ are respectively the same as defined for R¹′, R²′, nand Y²¹ in general formula (p1) described above in connection with the“acetal-type acid dissociable group”.

As examples of Y²², the same groups as those described above for Y²² ingeneral formula (a1-0-2) can be given.

Specific examples of structural units represented by general formula(a1-1) to (a1-4) are shown below.

In the formulas shown below, R^(α) represents a hydrogen atom, a methylgroup or a trifluoromethyl group.

As the structural unit (a1), structural units represented by generalformula (a1-1), (a1-2) or (a1-3) are preferable. More specifically, atleast one structural unit selected from the group consisting ofstructural units represented by formulas (a1-1-1) to (a-1-1-4),(a1-1-20) to (a1-1-23), (a1-2-1) to (a1-2-24) and (a1-3-25) to (a1-3-28)is more preferable.

Further, as the structural unit (a1), structural units represented bygeneral formula (a1-1-01) shown below which includes the structuralunits represented by formulas (a1-1-1) to (a1-1-3) and (a1-1-26),structural units represented by general formula (a1-1-02) shown belowwhich includes the structural units represented by formulas (a1-1-16),(a1-1-17), (a1-1-20) to (a1-1-23) and (a1-1-32), structural unitsrepresented by general formula (a1-3-01) shown below which include thestructural units represented by formulas (a1-3-25) and (a1-3-26),structural units represented by general formula (a1-3-02) shown belowwhich include the structural units represented by formulas (a1-3-27) and(a1-3-28), and structural units represented by general formula (a1-3-03)shown below which include the structural units represented by formulas(a1-3-29) and (a1-3-30) are also preferable.

In the formulas, each R independently represents a hydrogen atom, analkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to5 carbon atoms; represents an alkyl group of 1 to 5 carbon atoms; R¹²represents an alkyl group of 1 to 7 carbon atoms; and h represents aninteger of 1 to 6.

In general formula (a1-1-01), R is the same as defined above. The alkylgroup of 1 to 5 carbon atoms for R¹¹ is the same as defined for thealkyl group of 1 to 5 carbon atoms for R, and a methyl group, an ethylgroup or an isopropyl group is preferable.

In general formula (a1-1-02), R is the same as defined above. The alkylgroup of 1 to 5 carbon atoms for R¹² is the same as defined for thealkyl group of 1 to 5 carbon atoms for R, and a methyl group, an ethylgroup or an isopropyl group is preferable. h is preferably 1 or 2, andmost preferably 2.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R¹⁴ isthe same as defined above; R¹³ represents a hydrogen atom or a methylgroup; and a represents an integer of 1 to 10.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R¹⁴ isthe same as defined above; R¹³ represents a hydrogen atom or a methylgroup; a represents an integer of 1 to 10; and n′ represents an integerof 1 to 6.

In the formula, R is the same as defined above; each of Y²′ and Y²″independently represents a divalent linking group; X′ represents an aciddissociable group; and n represents an integer of 0 to 3.

In general formulas (a1-3-01) to (a1-3-03), R is the same as definedabove.

R¹³ is preferably a hydrogen atom.

n′ is preferably 1 or 2, and most preferably 2.

a is preferably an integer of 1 to 8, more preferably an integer of 2 to5, and most preferably 2.

As the divalent linking group for Y²′ and Y²″, the same groups as thosedescribed above for Y²² in general formula (a1-3) can be used.

As Y²′, a divalent hydrocarbon group which may have a substituent ispreferable, a linear aliphatic hydrocarbon group is more preferable, anda linear alkylene group is still more preferable. Among linear alkylenegroups, a linear alkylene group of 1 to 5 carbon atoms is preferable,and a methylene group or an ethylene group is particularly desirable.

As Y²″, a divalent hydrocarbon group which may have a substituent ispreferable, a linear aliphatic hydrocarbon group is more preferable, anda linear alkylene group is still more preferable. Among linear alkylenegroups, a linear alkylene group of 1 to 5 carbon atoms is preferable,and a methylene group or an ethylene group is particularly desirable.

As the acid dissociable group for X′, the same groups as those describedabove can be used. X′ is preferably a tertiary alkyl ester-type aciddissociable group, more preferably the aforementioned group which has atertiary carbon atom on the ring structure of a cyclic alkyl group.Among the aforementioned groups, groups represented by theaforementioned general formulas (1-1) to (1-9) are preferable.

n represents an integer of 0 to 3, preferably an integer of 0 to 2, morepreferably 0 or 1, and most preferably 1.

Furthermore, as the structural unit (a1), a structural unit (a1-5)represented by general formula (a1-5) is also preferable.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R³represents a single bond or a divalent linking group; Y⁰ represents analiphatic hydrocarbon group which may have a substituent; OZ representsan acid decomposable group; a represents an integer of 1 to 3 and brepresents an integer of 0 to 2, provided that a+b=1 to 3; and each of dand e independently represents an integer of 0 to 3.

In formula (a1-5), R is the same as defined above. As R, a hydrogen atomor a methyl group is preferable.

In formula (a1-5), R³ represents a single bond or a divalent linkinggroup. Examples of the divalent linking group for R³ include the samedivalent linking groups as those described above for Y²² in theaforementioned formula (a1-0-2).

In formula (a1-5), Y⁰ represents an aliphatic cyclic group. The term“aliphatic cyclic group” refers to a monocyclic group or polycyclicgroup that has no aromaticity.

The “aliphatic cyclic group” within the structural unit (a1-5) may ormay not have a substituent. Examples of the substituent include an alkylgroup of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl groupof 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents(aliphatic ring) is not limited to be constituted from only carbon andhydrogen (not limited to hydrocarbon rings), and the ring (aliphaticring) may contain an oxygen atom in the structure thereof. Further, the“hydrocarbon ring” may be either saturated or unsaturated, but ispreferably saturated.

The aliphatic cyclic group may be either a polycyclic group or amonocyclic group. Examples of aliphatic cyclic groups include groups inwhich two or more hydrogen atoms have been removed from amonocycloalkane or a polycycloalkane such as a bicycloalkane,tricycloalkane or tetracycloalkane which may or may not be substitutedwith an alkyl group of 1 to 5 carbon atoms, a fluorine atom or afluorinated alkyl group. Specific examples include groups in which twoor more hydrogen atoms have been removed from a monocycloalkane such ascyclopentane or cyclohexane; and groups in which two or more hydrogenatoms have been removed from a polycycloalkane such as adamantane,norbornane, isobornane, tricyclodecane or tetracyclododecane.

Further examples of the aliphatic cyclic group include groups in whichtwo or more hydrogen atoms have been removed from tetrahydrofuran ortetrahydropyran which may or may not be substituted with an alkyl groupof 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group.

The aliphatic cyclic group within the structural unit (a1-5) ispreferably a polycyclic group, and a group in which two or more hydrogenatoms have been removed from adamantane is particularly desirable.

In the aforementioned formula (a1-5), OZ represents an acid decomposablegroup.

As the acid decomposable group for OZ, an acid decomposable group whichis decomposed to form a hydroxy group (—OH) is preferable, and examplesthereof include (1) a group in which a hydroxy group is protected withan acetal-type acid dissociable group Z, and (2) a group in which Z hasa tertiary ester-type acid dissociable group within the structurethereof, and is further decomposed by a decarboxylation reaction afterthe acid dissociation.

The acetal-type acid dissociable group for Z within (1) “a group inwhich a hydroxy group is protected with an acetal-type acid dissociablegroup” is the same as defined above. As Z for the group (1), a1-n-butoxyethyl group (—CH(CH₃)—O—C₄H₉) or an n-butoxymethyl group(—CH₂—O—C₄H₉) is particularly desirable.

The oxygen atom within OZ is derived from the hydroxy group protectedwith the acetal-type acid dissociable group, and by the action of anacid, the bond between the oxygen atom and the acetal-type aciddissociable group is broken, so as to form a hydroxy group (—OH) whichis a polar group on the terminal of the structural unit.

In the (2) “group in which Z has a tertiary ester-type acid dissociablegroup within the structure thereof, and is further decomposed by adecarboxylation reaction after the acid dissociation”, the tertiaryester-type acid dissociable group is as described above, and thetertiary ester-type acid dissociable group is eliminated and carbondioxide is generated, so as to form a hydroxy group (—OH) which is apolar group on the terminal of the structural unit.

The alkyl group within the tertiary ester-type acid dissociable groupfor Z in OZ may be either an alkyl group which does not have a ringstructure (chain-like structure), or an alkyl group having a ringstructure.

In the case of a chain-like alkyl group, as Z for OZ, a chain-liketertiary alkyloxycarbonyl group represented by general formula (II)shown below can be mentioned.

In formula (II), each of R²¹ to R²³ independently represents a linear orbranched alkyl group. The number of carbon atoms within the alkyl groupis preferably from 1 to 5, and more preferably from 1 to 3.

Further, in the group represented by —C(R²¹)(R²²)(R²³) in generalformula (II), the total number of carbon atoms is preferably from 4 to7, more preferably from 4 to 6, and most preferably 4 or 5.

Preferable examples of the group represented by —C(R²¹)(R²²)(R²³) ingeneral formula (II) include a tert-butyl group and a tert-pentyl group,and a tert-butyl group is more preferable. That is, in such a case, asZ, a tert-butyloxycarbonyl group (t-boc) and a tert-pentyloxycarbonylgroup are preferable.

Furthermore, in the case where the acid decomposable group OZ is (3) agroup which does not form a hydroxy group (—OH) after being decomposed(e.g., a group which forms a carboxy group), as Z for OZ, a tertiaryalkyloxycarbonylalkyl group represented by general formula (III) shownbelow is preferable.

In general formula (III), R²¹ to R²³ are the same as defined for R²¹ toR²³ in general formula (II).

f represents an integer of 1 to 3, and is preferably 1 or 2.

As the chain-like tertiary alkyloxycarbonylalkyl group, atert-butyloxycarbonylmethyl group and a tert-butyloxycarbonylethyl groupare preferable.

Among these, as the tertiary alkyl group-containing group which does nothave a ring structure, a tertiary alkyloxycarbonyl group or a tertiaryalkyloxycarbonylalkyl group is preferable, a tertiary alkyloxycarbonylgroup is more preferable, and a tert-butyloxycarbonyl group (t-boc) ismost preferable.

In the case where Z is a group having in the structure thereof atertiary alkyl ester-type acid dissociable group containing a ringstructure, as examples of Z for OZ, groups in which the terminal oxygenatom of —C(═O)—O— or —(CH₂)₁—C(═O)—O— (f is the same as defined for f informula (III)) has bonded thereto a group represented by any of theaforementioned formulae (1-1) to (1-9) and (2-1) to (2-6) can be given.

Among the above examples, as OZ, a group (1) or (2) which forms ahydroxy group (—OH) after being decomposed is preferable, a group inwhich Z is a group represented by the aforementioned general formula(II) is more preferable, and a group in which Z represents atert-butyloxycarbonyl group (t-boc) or a 1,1-dimethylpropoxycarbonylgroup is most preferable.

In general formula (a1-5), a represents an integer of 1 to 3, and brepresents an integer of 0 to 2, provided that a+b=1 to 3.

a is preferably 1 or 2, and more preferably 1.

b is preferably 0.

a+b is preferably 1 or 2, and more preferably 1.

d represents an integer of 0 to 3, preferably 0 or 1, and morepreferably 0.

e represents an integer of 0 to 3, preferably 0 or 1, and morepreferably 0.

When b is 1 or more, the structural unit (a1-5) falls under thedefinition of the structural unit (a3) described later. However, astructural unit represented by general formula (a1-5) is regarded as astructural unit (a1-5), and not as a structural unit (a3).

In particular, as the structural unit (a1-5), a structural unitrepresented by general formula (a11-1-1), (a11-1-2) or (a11-2) shownbelow is preferable, and a structural unit represented by generalformula (a11-1-1) is more preferable.

In the formula, R, Z, b, c, d and e are the same as defined above.

In the formula, R, Z, b, c, d and e are respectively the same as definedabove, and the plurality of e and Z may be the same or different fromeach other.

In the formula, R, Z, a, b, c, d and e are the same as defined above;and C″ represents an integer of 1 to 3.

In formula (a11-2), c″ represents an integer of 1 to 3, preferably 1 or2, and still more preferably 1.

When c represents 0 in formula (a11-2), the oxygen atom on the terminalof the carbonyloxy group within the acrylate ester is preferably notbonded to the carbon atom which is bonded to the oxygen atom within thecyclic group. That is, when c represents 0, it is preferable that thereare at least two carbon atoms present between the terminal oxygen atomand the oxygen atom within the cyclic group (excluding the case wherethe number of such carbon atom is one (i.e., the case where an acetalbond is formed)).

A monomer for deriving the structural unit (a11-1) can be synthesized,for example, by protecting part or all of the hydroxyl groups within acompound represented by general formula (a11-0) shown below (namely, anacrylate ester containing an aliphatic cyclic group having 1 to 3alcoholic hydroxyl groups) with alkoxyalkyl groups the aforementioned Zby a conventional method.

In the formula, R, Y⁰, a, b, c, d and e are the same as defined above.

In the component (A1), the amount of the structural unit (a1) based onthe combined total of all structural units constituting the component(A1) is preferably 5 to 90 mol %, more preferably 10 to 85 mol %, andstill more preferably 15 to 80 mol %. When the amount of the structuralunit (a1) is at least as large as the lower limit of the above-mentionedrange, a pattern can be easily formed using a resist compositionprepared from the component (A1). On the other hand, when the amount ofthe structural unit (a1)) is no more than the upper limit of theabove-mentioned range, a good balance can be achieved with the otherstructural units.

(Structural Unit (a2))

The structural unit (a2) is at least one structural unit selected fromthe group consisting of a structural unit derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains an —SO₂—containing cyclic group (hereafter, referred to as “structural unit(a2^(S))”), and a structural unit derived from an acrylate ester whichmay have the hydrogen atom bonded to the carbon atom on the α-positionsubstituted with a substituent and contains a lactone-containing cyclicgroup (hereafter, referred to as “structural unit (a2^(L))”).

By virtue of the structural unit (a2) containing a —SO₂— containingcyclic group or a lactone-containing cyclic group, a resist compositioncontaining the component (A1) including the structural unit (a2) iscapable of improving the adhesion of a resist film to a substrate, andincreasing the compatibility with the developing solution containingwater (especially in the case of alkali developing process), therebycontributing to improvement of lithography properties.

Structural Unit (a2^(S)):

The structural unit (a2^(S)) is a structural unit derived from anacrylate ester containing a —SO₂— containing cyclic group and which mayhave the hydrogen atom bonded to the carbon atom on the α-positionsubstituted with a substituent.

Here, an “—SO₂— containing cyclic group” refers to a cyclic group havinga ring containing —SO₂— within the ring structure thereof, i.e., acyclic group in which the sulfur atom (S) within —SO₂— forms part of thering skeleton of the cyclic group. The ring containing —SO₂— within thering skeleton thereof is counted as the first ring. A cyclic group inwhich the only ring structure is the ring that contains —SO₂— in thering skeleton thereof is referred to as a monocyclic group, and a groupcontaining other ring structures is described as a polycyclic groupregardless of the structure of the other rings. The —SO₂— containingcyclic group may be either a monocyclic group or a polycyclic group.

As the —SO₂— containing cyclic group, a cyclic group containing —O—SO₂—within the ring skeleton thereof, i.e., a cyclic group containing asultone ring in which —O—S— within the —O—SO₂— group forms part of thering skeleton thereof is particularly desirable.

The —SO₂— containing cyclic group preferably has 3 to 30 carbon atoms,more preferably 4 to 20, still more preferably 4 to 15, and mostpreferably 4 to 12. Herein, the number of carbon atoms refers to thenumber of carbon atoms constituting the ring skeleton, excluding thenumber of carbon atoms within a substituent.

The —SO₂— containing cyclic group may be either a —SO₂— containingaliphatic cyclic group or a —SO₂— containing aromatic cyclic group. A—SO₂— containing aliphatic cyclic group is preferable.

Examples of the —SO₂— containing aliphatic cyclic group includealiphatic cyclic groups in which part of the carbon atoms constitutingthe ring skeleton has been substituted with a —SO₂— group or a —O—SO₂—group and has at least one hydrogen atom removed from the aliphatichydrocarbon ring. Specific examples include an aliphatic hydrocarbonring in which a —CH₂— group constituting the ring skeleton thereof hasbeen substituted with a —SO₂— group and has at least one hydrogen atomremoved therefrom; and an aliphatic hydrocarbon ring in which a—CH₂—CH₂— group constituting the ring skeleton has been substituted witha —O—SO₂— group and has at least one hydrogen atom removed therefrom.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, andmore preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or apolycyclic group. As the monocyclic group, a group in which two hydrogenatoms have been removed from a monocycloalkane of 3 to 6 carbon atoms ispreferable. Examples of the monocycloalkane include cyclopentane andcyclohexane. As the polycyclic group, a group in which two hydrogenatoms have been removed from a polycycloalkane of 7 to 12 carbon atomsis preferable. Examples of the polycycloalkane include adamantane,norbornane, isobornane, tricyclodecane and tetracyclododecane.

The —SO₂— containing cyclic group may have a substituent. Examples ofthe substituent include an alkyl group, an alkoxy group, a halogen atom,a halogenated alkyl group, a hydroxy group, an oxygen atom (═O),—OC(═O)R″, a hydroxyalkyl group and a cyano group.

The alkyl group for the substituent is preferably an alkyl group of 1 to6 carbon atoms. Further, the alkyl group is preferably a linear alkylgroup or a branched alkyl group. Specific examples include a methylgroup, an ethyl group, a propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a tert-butyl group, a pentyl group, anisopentyl group, a neopentyl group and a hexyl group. Among these, amethyl group or ethyl group is preferable, and a methyl group isparticularly desirable.

As the alkoxy group for the substituent, an alkoxy group of 1 to 6carbon atoms is preferable. Further, the alkoxy group is preferably alinear or branched alkoxy group. Specific examples of the alkoxy groupinclude the aforementioned alkyl groups for the substituent having anoxygen atom (—O—) bonded thereto.

Examples of the halogen atom for the substituent include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom, and a fluorineatom is preferable.

Examples of the halogenated alkyl group for the substituent includegroups in which part or all of the hydrogen atoms within theaforementioned alkyl groups has been substituted with the aforementionedhalogen atoms.

As examples of the halogenated alkyl group for the substituent, groupsin which part or all of the hydrogen atoms of the aforementioned alkylgroups for the substituent have been substituted with the aforementionedhalogen atoms can be given. As the halogenated alkyl group, afluorinated alkyl group is preferable, and a perfluoroalkyl group isparticularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ represents a hydrogenatom or a linear, branched or cyclic alkyl group of 1 to 15 carbonatoms.

When R″ represents a linear or branched alkyl group, it is preferably analkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and mostpreferably 5 to 10 carbon atoms. As examples of the cycloalkyl group,groups in which one or more hydrogen atoms have been removed from amonocycloalkane or a polycycloalkane such as a bicycloalkane,tricycloalkane or tetracycloalkane, which may or may not be substitutedwith a fluorine atom or a fluorinated alkyl group, may be used. Specificexamples include groups in which one or more hydrogen atoms have beenremoved from a monocycloalkane such as cyclopentane and cyclohexane; andgroups in which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

The hydroxyalkyl group for the substituent preferably has 1 to 6 carbonatoms, and specific examples thereof include the aforementioned alkylgroups for the substituent in which at least one hydrogen atom has beensubstituted with a hydroxy group.

More specific examples of the —SO₂— containing cyclic group includegroups represented by general formulas (3-1) to (3-4) shown below.

In the formulas, A′ represents an oxygen atom, a sulfur atom or analkylene group of 1 to 5 carbon atoms which may contain an oxygen atomor a sulfur atom; z represents an integer of 0 to 2; and R²⁷ representsan alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxylgroup, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, whereinR″ represents a hydrogen atom or an alkyl group.

In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom(—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atomswhich may contain an oxygen atom or a sulfur atom.

As the alkylene group of 1 to 5 carbon atoms represented by A′, a linearor branched alkylene group is preferable, and examples thereof include amethylene group, an ethylene group, an n-propylene group and anisopropylene group.

Examples of alkylene groups that contain an oxygen atom or a sulfur atominclude the aforementioned alkylene groups in which —O— or —S— is bondedto the terminal of the alkylene group or present between the carbonatoms of the alkylene group. Specific examples of such alkylene groupsinclude —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂—, —CH₂—S—CH₂—.

As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable,more preferably an alkylene group of 1 to 5 carbon atoms, and mostpreferably a methylene group.

z represents an integer of 0 to 2, and is most preferably 0.

When z is 2, the plurality of R²⁷ may be the same or different from eachother.

As the alkyl group, alkoxy group, halogenated alkyl group, —COOR″,—OC(═O)R″ and hydroxyalkyl group for R²⁷, the same alkyl groups, alkoxygroups, halogenated alkyl groups, —COOR″, —OC(═O)R″ and hydroxyalkylgroups as those described above as the substituent for the —SO₂—containing cyclic group can be mentioned.

Specific examples of the cyclic groups represented by general formulas(3-1) to (3-4) are shown below. In the formulas shown below, “Ac”represents an acetyl group.

As the —SO₂— containing cyclic group, a group represented by theaforementioned general formula (3-1) is preferable, at least one memberselected from the group consisting of groups represented by theaforementioned chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1)is more preferable, and a group represented by chemical formula (3-1-1)is most preferable.

More specific examples of the structural unit (a2^(S)) includestructural units represented by general formula (a2-0) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²⁸represents a —SO₂— containing cyclic group; and R²⁹ represents a singlebond or a divalent linking group.

In genera formula (a2-0), R is the same as defined above.

R²⁸ is the same as defined for the aforementioned —SO₂— containinggroup.

R²⁹ may be either a single bond or a divalent linking group, but adivalent linking group is preferable.

The divalent linking group for R²⁹ is not particularly limited, andexamples thereof include the same divalent linking groups as thosedescribed above for Y²² in the aforementioned formula (a1-0-2). Amongthese, an alkylene group or a divalent linking group containing an esterbond (—C(═O)—O—) is preferable.

As the alkylene group, a linear or branched alkylene group ispreferable. Specific examples include the same linear alkylene groupsand branched alkylene groups as those described above for the aliphatichydrocarbon group represented by Y²².

As the divalent linking group containing an ester bond, a grouprepresented by general formula: —R³⁰—C(═O)—O— (in the formula, R³⁰represents a divalent linking group) is particularly desirable. That is,the structural unit (a2^(S)) is preferably a structural unit representedby general formula (a2-0-1) shown below.

In the formula, R and R²⁸ are the same as defined above; and R³⁰represents a divalent linking group.

R³⁰ is not particularly limited, and examples thereof include the samedivalent linking groups as those described above for Y²² in theaforementioned formula (a1-0-2).

As the divalent linking group for R³⁰, an alkylene group, a divalentalicyclic hydrocarbon group or a divalent linking group containing ahetero atom is preferable.

As the linear or branched alkylene group, the divalent alicyclichydrocarbon group and the divalent linking group containing a heteroatom, the same linear or branched alkylene group, cyclic aliphatichydrocarbon group and divalent linking group containing a hetero atom asthose described above for Y²² can be mentioned.

Among these, a linear or branched alkylene group, or a divalent linkinggroup containing an oxygen atom as a hetero atom is more preferable.

As the linear alkylene group, a methylene group or an ethylene group ispreferable, and a methylene group is particularly desirable.

As the branched alkylene group, an alkylmethylene group or analkylethylene group is preferable, and —CH(CH₃)—, —C(CH₃)₂— or—C(CH₃)₂CH₂— is particularly desirable.

As the divalent linking group containing a hetero atom, a divalentlinking group containing an ether bond or an ester bond is preferable,and a group represented by the aforementioned formula -A-O—B—,-[A-C(═O)—O]_(m)—B— or -A-O—C(═O)—B— is more preferable.

Among these, a group represented by the formula -A-O—C(═O)—B— ispreferable, and a group represented by the formula:—(CH₂)_(c1)—C(═O)—O—(CH₂)_(d1)— is particularly desirable. c1 representsan integer of 1 to 5, and preferably 1 or 2. d1 represents an integer of1 to 5, and preferably 1 or 2.

In particular, as the structural unit (a2⁵), a structural unitrepresented by general formula (a0-1-11) or (a0-1-12) shown below ispreferable, and a structural unit represented by general formula(a0-1-12) shown below is more preferable.

In the formulas, R, A′, R²⁷, z and R³⁰ are the same as defined above.

In general formula (a0-1-11), A′ is preferably a methylene group, anoxygen atom (—O—) or a sulfur atom (—S—).

As R³⁰, a linear or branched alkylene group or a divalent linking groupcontaining an oxygen atom is preferable. As the linear or branchedalkylene group and the divalent linking group containing an oxygen atomrepresented by R³⁰, the same linear or branched alkylene groups and thedivalent linking groups containing an oxygen atom as those describedabove can be mentioned.

As the structural unit represented by general formula (a0-1-12), astructural unit represented by general formula (a0-1-12a) or (a0-1-12b)shown below is particularly desirable.

In the formulas, R and A′ are the same as defined above; and each of c′to e′ independently represents an integer of 1 to 3.

Structural Unit (a2^(L)):

The structural unit (a2^(L)) is a structural unit derived from anacrylate ester which may have the hydrogen atom bonded to the carbonatom on the α-position substituted with a substituent and contains alactone-containing cyclic group.

The term “lactone-containing cyclic group” refers to a cyclic groupincluding a ring containing a —O—C(O)— structure (lactone ring). Theterm “lactone ring” refers to a single ring containing a —O—C(O)—structure, and this ring is counted as the first ring. Alactone-containing cyclic group in which the only ring structure is thelactone ring is referred to as a monocyclic group, and groups containingother ring structures are described as polycyclic groups regardless ofthe structure of the other rings. The lactone-containing cyclic groupmay be either a monocyclic group or a polycyclic group.

The lactone-containing cyclic group for the structural unit (a2^(L)) isnot particularly limited, and an arbitrary structural unit may be used.Specific examples of lactone-containing monocyclic groups include agroup in which one hydrogen atom has been removed from a 4- to6-membered lactone ring, such as a group in which one hydrogen atom hasbeen removed from β-propionolatone, a group in which one hydrogen atomhas been removed from γ-butyrolactone, and a group in which one hydrogenatom has been removed from δ-valerolactone. Further, specific examplesof lactone-containing polycyclic groups include groups in which onehydrogen atom has been removed from a lactone ring-containingbicycloalkane, tricycloalkane or tetracycloalkane.

Examples of the structural unit (a2^(L)) include structural unitsrepresented by the aforementioned general formula (a2-0) in which theR²⁸ group has been substituted with a lactone-containing cyclic group.Specific examples include structural units represented by generalformulas (a2-1) to (a2-5) shown below.

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; eachR′ independently represents a hydrogen atom, an alkyl group of 1 to 5carbon atoms, an alkoxy group of 1 to 5 carbon atoms or —COOR″, whereinR″ represents a hydrogen atom or an alkyl group; R²⁹ represents a singlebond or a divalent linking group; s″ represents an integer of 0 to 2; A″represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5carbon atoms which may contain an oxygen atom or a sulfur atom; and mrepresents 0 or 1.

In general formulas (a2-1) to (a2-5), R is the same as defined above.

Examples of the alkyl group of 1 to 5 carbon atoms for R′ include amethyl group, an ethyl group, a propyl group, an n-butyl group and atert-butyl group.

Examples of the alkoxy group of 1 to 5 carbon atoms for R′ include amethoxy group, an ethoxy group, an n-propoxy group, an iso-propoxygroup, an n-butoxy group and a tert-butoxy group

In terms of industrial availability, R′ is preferably a hydrogen atom.

The alkyl group for R″ may be any of linear, branched or cyclic.

When R″ is a linear or branched alkyl group, it preferably has 1 to 10carbon atoms, more preferably 1 to 5 carbon atoms.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and mostpreferably 5 to 10 carbon atoms. As examples of the cycloalkyl group,groups in which one or more hydrogen atoms have been removed from amonocycloalkane or a polycycloalkane such as a bicycloalkane,tricycloalkane or tetracycloalkane, which may or may not be substitutedwith a fluorine atom or a fluorinated alkyl group, may be used. Examplesof such groups include groups in which one or more hydrogen atoms havebeen removed from a monocycloalkane such as cyclopentane or cyclohexane;and groups in which one or more hydrogen atoms have been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

As examples of A″, the same groups as those described above for A′ ingeneral formula (3-1) can be given. A″ is preferably an alkylene groupof 1 to 5 carbon atoms, an oxygen atom (—O—) or a sulfur atom (—S—), andmore preferably an alkylene group of 1 to 5 carbon atoms or —O—. As thealkylene group of 1 to 5 carbon atoms, a methylene group or adimethylethylene group is preferable, and a methylene group isparticularly desirable.

R²⁹ is the same as defined for R²⁹ in the aforementioned general formula(a2-0).

In formula (a2-1), s″ is preferably 1 or 2.

Specific examples of structural units represented by general formulas(a2-1) to (a2-5) are shown below. In the formulas shown below, R^(α)represents a hydrogen atom, a methyl group or a trifluoromethyl group.

As the structural unit (a2^(L)), it is preferable to include at leastone structural unit selected from the group consisting of structuralunits represented by the aforementioned general formulas (a2-1) to(a2-5), more preferably at least one structural unit selected from thegroup consisting of structural units represented by the aforementionedgeneral formulas (a2-1) to (a2-3), and most preferably at least onestructural unit selected from the group consisting of structural unitsrepresented by the aforementioned general formulas (a2-1) and (a2-3).

Specifically, it is preferable to use at least one structural unitselected from the group consisting of formulas (a2-1-1), (a2-1-2),(a2-2-1), (a2-2-7), (a2-2-12), (a2-2-14), (a2-3-1) and (a2-3-5).

In the component (A1), as the structural unit (a2), one type ofstructural unit may be used, or two or more types may be used incombination. For example, as the structural unit (a2), a structural unit(a2^(S)) may be used alone, or a structural unit (a2^(L)), or acombination of these structural units may be used. Further, as thestructural unit (a2^(S)) or the structural unit (a2^(L)), either asingle type of structural unit may be used, or two or more types may beused in combination.

When the component (A1) contains the structural unit (a2), the amount ofthe structural unit (a2) based on the combined total of all structuralunits constituting the component (A1) is preferably 1 to 80 mol %, morepreferably 10 to 75 mol %, still more preferably 10 to 70 mol %, andmost preferably 15 to 60 mol %. When the amount of the structural unit(a2) is at least as large as the lower limit of the above-mentionedrange, the effect of using the structural unit (a2) can besatisfactorily achieved. On the other hand, when the amount of thestructural unit (a2) is no more than the upper limit of theabove-mentioned range, a good balance can be achieved with the otherstructural units, and various lithography properties such as DOF and CDUand pattern shape can be improved.

(Structural Unit (a3))

The structural unit (a3) is a structural unit derived from an acrylateester which may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent and contains a polargroup-containing aliphatic hydrocarbon group.

When the component (A1) includes the structural unit (a3), thehydrophilicity of the component (A1) is enhanced, thereby contributingto improvement in resolution.

Examples of the polar group include a hydroxyl group, cyano group,carboxyl group, or hydroxyalkyl group in which part of the hydrogenatoms of the alkyl group have been substituted with fluorine atoms,although a hydroxyl group is particularly desirable.

Examples of the aliphatic hydrocarbon group include linear or branchedhydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms,and polycyclic aliphatic hydrocarbon groups (polycyclic groups).

These polycyclic groups can be selected appropriately from the multitudeof groups that have been proposed for the resins of resist compositionsdesigned for use with ArF excimer lasers. The polycyclic grouppreferably has 7 to 30 carbon atoms.

Of the various possibilities, structural units derived from an acrylateester that include an aliphatic polycyclic group that contains ahydroxyl group, cyano group, carboxyl group or a hydroxyalkyl group inwhich part of the hydrogen atoms of the alkyl group have beensubstituted with fluorine atoms are particularly desirable. Examples ofthe polycyclic group include groups in which two or more hydrogen atomshave been removed from a bicycloalkane, tricycloalkane, tetracycloalkaneor the like. Specific examples include groups in which two or morehydrogen atoms have been removed from a polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane ortetracyclododecane. Of these polycyclic groups, groups in which two ormore hydrogen atoms have been removed from adamantane, norbornane ortetracyclododecane are preferred industrially.

When the aliphatic hydrocarbon group within the polar group-containingaliphatic hydrocarbon group is a linear or branched hydrocarbon group of1 to 10 carbon atoms, the structural unit (a3) is preferably astructural unit derived from a hydroxyethyl ester of acrylic acid. Onthe other hand, when the hydrocarbon group is a polycyclic group,structural units represented by formulas (a3-1), (a3-2) and (a3-3) shownbelow are preferable.

In the formulas, R is the same as defined above; j is an integer of 1 to3; k is an integer of 1 to 3; t′ is an integer of 1 to 3; l is aninteger of 1 to 5; and s is an integer of 1 to 3.

In general formula (a3-1), j is preferably 1 or 2, and morepreferably 1. When j is 2, it is preferable that the hydroxyl groups bebonded to the 3rd and 5th positions of the adamantyl group. When j is 1,it is preferable that the hydroxyl group be bonded to the 3rd positionof the adamantyl group.

j is preferably 1, and it is particularly desirable that the hydroxylgroup be bonded to the 3rd position of the adamantyl group.

In formula (a3-2), k is preferably 1. The cyano group is preferablybonded to the 5th or 6th position of the norbornyl group.

In formula (a3-3), t′ is preferably 1. l is preferably 1. s ispreferably 1. Further, it is preferable that a 2-norbornyl group or3-norbornyl group be bonded to the terminal of the carboxy group of theacrylic acid. The fluorinated alkylalcohol is preferably bonded to the5th or 6th position of the norbornyl group.

As the structural unit (a3), one type of structural unit may be used, ortwo or more types may be used in combination.

In the component (A1), the amount of the structural unit (a3) based onthe combined total of all structural units constituting the component(A1) is preferably 1 to 50 mol %, more preferably 3 to 45 mol %, andstill more preferably 5 to 40 mol %. When the amount of the structuralunit (a3) is at least as large as the lower limit of the above-mentionedrange, the effect of using the structural unit (a3) can besatisfactorily achieved. On the other hand, when the amount of thestructural unit (a3) is no more than the upper limit of theabove-mentioned range, a good balance can be achieved with the otherstructural units.

(Other Structural Units)

The component (A1) may also have a structural unit other than theabove-mentioned structural units (a1) to (a3) (hereafter, referred to as“structural unit (a4)”), as long as the effects of the present inventionare not impaired.

As the structural unit (a4), any other structural unit which cannot beclassified as one of the above structural units (a1) to (a3) can be usedwithout any particular limitation, and any of the multitude ofconventional structural units used within resist resins for ArF excimerlasers or KrF excimer lasers (and particularly for ArF excimer lasers)can be used.

Preferable examples of the structural unit (a4) include (1) a structuralunit derived from an acrylate ester which contains anon-acid-dissociable aliphatic polycyclic group and may have thehydrogen atom bonded to the carbon atom on the α-position substitutedwith a substituent, (2) a structural unit derived from an acrylate esterwhich may have the hydrogen atom bonded to the carbon atom on theα-position substituted with a substituent, (3) a structural unit derivedfrom a styrene monomer and/or a vinylnaphthalene monomer, and (4) astructural unit derived from a hydroxystyrene monomer and/or avinyl(hydroxynaphthalene)monomer. Examples of this polycyclic groupinclude the same groups as those described above in relation to theaforementioned structural unit (a1), and any of the multitude ofconventional polycyclic groups used within the resin component of resistcompositions for ArF excimer lasers or KrF excimer lasers (andparticularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least onepolycyclic group selected from amongst a tricyclodecanyl group,adamantyl group, tetracyclododecanyl group, isobornyl group, andnorbornyl group is particularly desirable. These polycyclic groups maybe substituted with a linear or branched alkyl group of 1 to 5 carbonatoms.

Specific examples of the structural unit (a4) include units withstructures represented by general formulas (a4-1) to (a4-6) shown below.

In the formulas, R is the same as defined above.

As the structural unit (a4), one type of structural unit may be used, ortwo or more types may be used in combination.

When the component (A1) includes the structural unit (a4), the amount ofthe structural unit (a4) based on the combined total of all structuralunits constituting the component (A1) is preferably 1 to 20 mol %, morepreferably 1 to 15 mol %, and still more preferably 1 to 10 mol %. Whenthe amount of the structural unit (a4) is within the above-mentionedrange, both obtaining excellent lithography properties and adjusting thedissolution rate can be achieved.

The component (A1) is a copolymer including the structural unit (a1).

Examples of such copolymers include a copolymer consisting of thestructural units (a1) and (a2), a copolymer consisting of the structuralunits (a1) and (a3), and a copolymer consisting of the structural units(a1), (a2) and (a3).

In the present invention, as the component (A1), a copolymer thatincludes a combination of structural units represented by formula(A1-11) or (A1-12) shown below is particularly desirable. In generalformulas shown below, R, R²⁹, s″, R¹¹, j, c, e, Z, e′ and A′ are thesame as defined above, and the plurality of R may be the same ordifferent.

The weight average molecular weight (Mw) (the polystyrene equivalentvalue determined by gel permeation chromatography) of the component (A1)is not particularly limited, but is preferably 1,000 to 50,000, morepreferably 1,500 to 30,000, still more preferably 2,500 to 20,000, stillmore preferably 6,000 to 15,000, and most preferably 7,000 to 12,000.When the weight average molecular weight is no more than the upper limitof the above-mentioned range, the resist composition exhibits asatisfactory solubility in a resist solvent. On the other hand, when theweight average molecular weight is at least as large as the lower limitof the above-mentioned range, dry etching resistance and thecross-sectional shape of the resist pattern becomes satisfactory. Inaddition, since the weight average molecular weight has relationshipwith the dissolution rate in a developing solution, when the weightaverage molecular weight is within the range of 6,000 to 15,000, thedissolution rate of the component (A1) can be appropriately adjusted.

Further, the dispersity (Mw/Mn) of the component (A1) is notparticularly limited, but is preferably 1.0 to 5.0, more preferably 1.0to 3.0, and most preferably 1.2 to 2.5.

Here, Mn is the number average molecular weight.

In the component (A), as the component (A1), one type may be used, ortwo or more types of compounds may be used in combination.

In the component (A), the amount of the component (A1) based on thetotal weight of the component (A) is preferably 25% by weight or more,more preferably 50% by weight or more, still more preferably 75% byweight or more, and may be even 100% by weight. When the amount of thecomponent (A1) is 25% by weight or more, various lithography propertiesare improved.

[Component (A2)]

In the resist composition used in the present invention, the component(A) may contain “a base component which exhibits changed solubility inan alkali developing solution under action of acid” other than thecomponent (A1) (hereafter, referred to as “component (A2)”).

As the component (A2), it is preferable to use a compound that has amolecular weight of at least 500 and less than 2,500, contains ahydrophilic group, and also contains an acid dissociable group describedabove in connection with the component (A1).

Specific examples include compounds containing a plurality of phenolskeletons in which a part of the hydrogen atoms within hydroxyl groupshave been substituted with the aforementioned acid dissociable groups.

Examples of the component (A2) include low molecular weight phenoliccompounds in which a portion of the hydroxyl group hydrogen atoms havebeen substituted with an aforementioned acid dissociable group, andthese types of compounds are known, for example, as sensitizers or heatresistance improvers for use in non-chemically amplified g-line ori-line resists.

Examples of these low molecular weight phenol compounds includebis(4-hydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane,2-(4-hydroxyphenyl)-2-(4′-hydroxyphenyl)propane,2-(2,3,4-trihydroxyphenyl)-2-(2′,3′,4′-trihydroxyphenyl)propane,tris(4-hydroxyphenyl)methane,bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,bis(4-hydroxy-3-methylphenyl)-3,4-dihydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-4-hydroxyphenylmethane,bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3,4-dihydroxyphenylmethane,1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene,and dimers, trimers, tetramers, pentamers and hexamers of formalincondensation products of phenols such as phenol, m-cresol, p-cresol andxylenol. Needless to say, the low molecular weight phenol compound isnot limited to these examples. In particular, a phenol compound having 2to 6 triphenylmethane skeletons is preferable in terms of resolution andLWR.

Also, there are no particular limitations on the acid dissociable group,and suitable examples include the groups described above.

As the component (A2), one type of resin may be used, or two or moretypes of resins may be used in combination.

In the resist composition used in the present invention, as thecomponent (A), one type may be used, or two or more types of compoundsmay be used in combination.

Of the examples shown above, as the component (A), it is preferable touse one containing the component (A1).

In the resist composition used in the present invention, the amount ofthe component (A) can be appropriately adjusted depending on thethickness of the resist film to be formed, and the like.

<Component (B)>

As the component (B), there is no particular limitation, and any of theknown acid generators used in conventional chemically amplified resistcompositions can be used. Examples of these acid generators arenumerous, and include onium salt acid generators such as iodonium saltsand sulfonium salts; oxime sulfonate acid generators; diazomethane acidgenerators such as bisalkyl or bisaryl sulfonyl diazomethanes andpoly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate acid generators;iminosulfonate acid generators; and disulfone acid generators.

As an onium salt acid generator, a compound represented by generalformula (b-1) or (b-2) shown below can be used.

In the formulas above, R¹″ to R³″, R⁵″ and R⁶″ each independentlyrepresent an aryl group or alkyl group, wherein two of R¹″ to R³″ may bebonded to each other to form a ring with the sulfur atom; and R⁴″represents an alkyl group, a halogenated alkyl group, an aryl group oran alkenyl group which may have a substituent, provided that at leastone of R¹″ to R³″ represents an aryl group, and at least one of R⁵″ andR⁶″ represents an aryl group.

In formula (b-1) R¹″ to R³″ each independently represents an aryl groupor an alkyl group. In formula (b-1), two of R¹″ to R³″ may be bonded toeach other to form a ring with the sulfur atom.

Further, among R¹″ to R³″, at least one group represents an aryl group.Among R¹″ to R³″, two or more groups are preferably aryl groups, and itis particularly desirable that all of R¹″ to R³″ are aryl groups.

The aryl group for R¹″ to R³″ is not particularly limited. For example,an aryl group having 6 to 20 carbon atoms may be used in which part orall of the hydrogen atoms of the aryl group may or may not besubstituted with alkyl groups, alkoxy groups, halogen atoms or hydroxylgroups.

The aryl group is preferably an aryl group having 6 to 10 carbon atomsbecause it can be synthesized at a low cost. Specific examples thereofinclude a phenyl group and a naphthyl group.

The alkyl group, with which hydrogen atoms of the aryl group may besubstituted, is preferably an alkyl group having 1 to 5 carbon atoms,and most preferably a methyl group, an ethyl group, a propyl group, ann-butyl group, or a tert-butyl group.

The alkoxy group, with which hydrogen atoms of the aryl group may besubstituted, is preferably an alkoxy group having 1 to 5 carbon atoms,more preferably a methoxy group, an ethoxy group, an n-propoxy group, aniso-propoxy group, an n-butoxy group or a tert-butoxy group, and mostpreferably a methoxy group or an ethoxy group.

The halogen atom, with which hydrogen atoms of the aryl group may besubstituted, is preferably a fluorine atom.

The alkyl group for R¹″ to R³″ is not particularly limited and includes,for example, a linear, branched or cyclic alkyl group having 1 to 10carbon atoms. In terms of achieving excellent resolution, the alkylgroup preferably has 1 to 5 carbon atoms. Specific examples thereofinclude a methyl group, an ethyl group, an n-propyl group, an isopropylgroup, an n-butyl group, an isobutyl group, an n-pentyl group, acyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group, anda decyl group, and a methyl group is most preferable because it isexcellent in resolution and can be synthesized at a low cost.

When two of R¹″ to R³″ in formula (b-1) are bonded to each other to forma ring with the sulfur atom, it is preferable that the two of R¹″ to R³″form a 3 to 10-membered ring including the sulfur atom, and it isparticularly desirable that the two of R¹″ to R³″ form a 5 to 7-memberedring including the sulfur atom.

When two of R¹″ to R³″ in formula (b-1) are bonded to each other to forma ring with the sulfur atom, the remaining one of R¹″ to R³″ ispreferably an aryl group. As examples of the aryl group, the same as theabove-mentioned aryl groups for R¹″ to R³″ can be given.

As preferable examples of the cation moiety for the compound representedby general formula (b-1), those represented by formulas (I-1-1) to(I-1-11) shown below can be given. Among these, a cation moiety having atriphenylmethane skeleton, such as a cation moiety represented by anyone of formulas (I-1-1) to (I-1-9) shown below is particularlydesirable.

In formulas (I-1-10) and (I-1-11), each of R⁹ and R¹⁰ independentlyrepresents a phenyl group or naphthyl group which may have asubstituent, an alkyl group of 1 to 5 carbon atoms, an alkoxy group or ahydroxy group.

u is an integer of 1 to 3, and most preferably 1 or 2.

R⁴″ represents an alkyl group, a halogenated alkyl group, an aryl groupor an alkenyl group which may have a substituent.

The alkyl group for R⁴″ may be any of linear, branched or cyclic.

The linear or branched alkyl group preferably has 1 to 10 carbon atoms,more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbonatoms.

The cyclic alkyl group preferably has 4 to 15 carbon atoms, morepreferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbonatoms.

As an example of the halogenated alkyl group for R⁴″, a group in whichpart of or all of the hydrogen atoms of the aforementioned linear,branched or cyclic alkyl group have been substituted with halogen atomscan be given. Examples of the aforementioned halogen atom include afluorine atom, a chlorine atom, a bromine atom and an iodine atom, and afluorine atom is preferable.

In the halogenated alkyl group, the percentage of the number of halogenatoms based on the total number of halogen atoms and hydrogen atoms(halogenation ratio (%)) is preferably 10 to 100%, more preferably 50 to100%, and most preferably 100%. Higher halogenation ratio is preferablebecause the acid strength increases.

The aryl group for R⁴″ is preferably an aryl group of 6 to 20 carbonatoms.

The alkenyl group for R⁴″ is preferably an alkenyl group of 2 to 10carbon atoms.

With respect to R⁴″, the expression “may have a substituent” means thatpart of or all of the hydrogen atoms within the aforementioned linear,branched or cyclic alkyl group, halogenated alkyl group, aryl group oralkenyl group may be substituted with substituents (atoms other thanhydrogen atoms, or groups).

R⁴″ may have one substituent, or two or more substituents.

Examples of the substituent include a halogen atom, a hetero atom, analkyl group, and a group represented by the formula X-Q¹- (in theformula, Q¹ represents a divalent linking group containing an oxygenatom; and X represents a hydrocarbon group of 3 to 30 carbon atoms whichmay have a substituent).

Examples of halogen atoms and alkyl groups as substituents for R⁴″include the same halogen atoms and alkyl groups as those described abovewith respect to the halogenated alkyl group for R⁴″.

Examples of hetero atoms include an oxygen atom, a nitrogen atom, and asulfur atom.

In the group represented by formula X-Q¹-, Q¹ represents a divalentlinking group containing an oxygen atom.

Q¹ may contain an atom other than oxygen. Examples of atoms other thanoxygen include a carbon atom, a hydrogen atom, a sulfur atom and anitrogen atom.

Examples of divalent linking groups containing an oxygen atom includenon-hydrocarbon, oxygen atom-containing linking groups such as an oxygenatom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond(—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond(—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon,hetero atom-containing linking groups with an alkylene group.

Specific examples of the combinations of the aforementionednon-hydrocarbon, hetero atom-containing linking groups and an alkylenegroup include —R⁹¹—O—, —R⁹²—O—C(═O)—, —C(═O)—O—R⁹³—O—C(═O)— (in theformulas, each of R⁹¹ to R⁹³ independently represents an alkylenegroup).

The alkylene group for R⁹¹ to R⁹³ is preferably a linear or branchedalkylene group, and preferably has 1 to 12 carbon atoms, more preferably1 to 5, and most preferably 1 to 3.

Specific examples of alkylene groups include a methylene group [—CH₂—];alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—,—C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)— and —C(CH₂CH₃)₂—; an ethylenegroup [—CH₂CH₂—]; alkylethylene groups such as —CH(CH₃)CH₂—,—CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂— and —CH(CH₂CH₃)CH₂—; a trimethylene group(n-propylene group) [—CH₂CH₂CH₂—]; alkyltrimethylene groups such as—CH(CH₃)CH₂CH₂— and —CH₂CH(CH₃)CH₂—; a tetramethylene group[—CH₂CH₂CH₂CH₂—]; alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—and —CH₂CH(CH₃)CH₂CH₂—; and a pentamethylene group [—CH₂CH₂CH₂CH₂CH₂—].

Q¹ is preferably a divalent linking group containing an ester linkage orether linkage, and more preferably a group of —R⁹¹—O—, —R⁹²—O—C(═O)— or—C(═O)—O—R⁹³—O—C(═O)—.

In the group represented by the formula X-Q¹-, the hydrocarbon group forX may be either an aromatic hydrocarbon group or an aliphatichydrocarbon group.

The aromatic hydrocarbon group is a hydrocarbon group having an aromaticring. The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms,more preferably 5 to 30, still more preferably 5 to 20, still morepreferably 6 to 15, and most preferably 6 to 12. Here, the number ofcarbon atoms within a substituent(s) is not included in the number ofcarbon atoms of the aromatic hydrocarbon group.

Specific examples of aromatic hydrocarbon groups include an aryl groupwhich is an aromatic hydrocarbon ring having one hydrogen atom removedtherefrom, such as a phenyl group, a biphenyl group, a fluorenyl group,a naphthyl group, an anthryl group or a phenanthryl group; and analkylaryl group such as a benzyl group, a phenethyl group, a1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethylgroup, or a 2-naphthylethyl group. The alkyl chain within the arylalkylgroup preferably has 1 to 4 carbon atom, more preferably 1 or 2, andmost preferably 1.

The aromatic hydrocarbon group may have a substituent. For example, partof the carbon atoms constituting the aromatic ring within the aromatichydrocarbon group may be substituted with a hetero atom, or a hydrogenatom bonded to the aromatic ring within the aromatic hydrocarbon groupmay be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbonatoms constituting the ring within the aforementioned aryl group hasbeen substituted with a hetero atom such as an oxygen atom, a sulfuratom or a nitrogen atom, and a heteroarylalkyl group in which part ofthe carbon atoms constituting the aromatic hydrocarbon ring within theaforementioned arylalkyl group has been substituted with theaforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbongroup, an alkyl group, an alkoxy group, a halogen atom, a halogenatedalkyl group, a hydroxyl group, an oxygen atom (═O) or the like can beused.

The alkyl group as the substituent for the aromatic hydrocarbon group ispreferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, anethyl group, a propyl group, an n-butyl group or a tert-butyl group isparticularly desirable.

The alkoxy group as the substituent for the aromatic hydrocarbon groupis preferably an alkoxy group having 1 to 5 carbon atoms, morepreferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxygroup, n-butoxy group or tert-butoxy group, and most preferably amethoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatichydrocarbon group include a fluorine atom, a chlorine atom, a bromineatom and an iodine atom, and a fluorine atom is preferable.

Example of the halogenated alkyl group as the substituent for thearomatic hydrocarbon group includes a group in which part or all of thehydrogen atoms within the aforementioned alkyl group have beensubstituted with the aforementioned halogen atoms.

The aliphatic hydrocarbon group for X may be either a saturatedaliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbongroup. Further, the aliphatic hydrocarbon group may be linear, branchedor cyclic.

In the aliphatic hydrocarbon group for X, part of the carbon atomsconstituting the aliphatic hydrocarbon group may be substituted with asubstituent group containing a hetero atom, or part or all of thehydrogen atoms constituting the aliphatic hydrocarbon group may besubstituted with a substituent group containing a hetero atom.

As the “hetero atom” for X, there is no particular limitation as long asit is an atom other than carbon and hydrogen. Examples of hetero atomsinclude a halogen atom, an oxygen atom, a sulfur atom and a nitrogenatom. Examples of the halogen atom include a fluorine atom, a chlorineatom, an iodine atom and a bromine atom.

The substituent group containing a hetero atom may consist of a heteroatom, or may be a group containing a group or atom other than a heteroatom.

Specific examples of the substituent group for substituting part of thecarbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—,—NH— (the H may be replaced with a substituent such as an alkyl group oran acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatichydrocarbon group is cyclic, the aliphatic hydrocarbon group may containany of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of thehydrogen atoms include an alkoxy group, a halogen atom, a halogenatedalkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1to 5 carbon atoms, more preferably a methoxy group, ethoxy group,n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group,and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, achlorine atom, a bromine atom and an iodine atom, and a fluorine atom ispreferable.

Example of the aforementioned halogenated alkyl group includes a groupin which part or all of the hydrogen atoms within an alkyl group of 1 to5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, ann-butyl group or a tert-butyl group) have been substituted with theaforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear or branched saturatedhydrocarbon group, a linear or branched monovalent unsaturatedhydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphaticcyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10.Specific examples include a methyl group, an ethyl group, a propylgroup, a butyl group, a pentyl group, a hexyl group, a heptyl group, anoctyl group, a nonyl group, a decyl group, an undecyl group, a dodecylgroup, a tridecyl group, an isotridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecylgroup, an octadecyl group, a nonadecyl group, an icosyl group, ahenicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to10. Specific examples include a 1-methylethyl group, a 1-methylpropylgroup, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutylgroup, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutylgroup, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentylgroup and a 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms,more preferably 2 to 5, still more preferably 2 to 4, and mostpreferably 3. Examples of linear monovalent unsaturated hydrocarbongroups include a vinyl group, a propenyl group (an allyl group) and abutynyl group. Examples of branched monovalent unsaturated hydrocarbongroups include a 1-methylpropenyl group and a 2-methylpropenyl group.

Among the above-mentioned examples, as the unsaturated hydrocarbongroup, a propenyl group is particularly desirable.

The aliphatic cyclic group may be either a monocyclic group or apolycyclic group. The aliphatic cyclic group preferably has 3 to 30carbon atoms, more preferably 5 to 30, still more preferably 5 to 20,still more preferably 6 to 15, and most preferably 6 to 12.

As the aliphatic cyclic group, a group in which one or more hydrogenatoms have been removed from a monocycloalkane or a polycycloalkane suchas a bicycloalkane, tricycloalkane or tetracycloalkane can be used.Specific examples include groups in which one or more hydrogen atomshave been removed from a monocycloalkane such as cyclopentane orcyclohexane; and groups in which one or more hydrogen atoms have beenremoved from a polycycloalkane such as adamantane, norbornane,isobornane, tricyclodecane or tetracyclododecane.

When the aliphatic cyclic group does not contain a heteroatom-containing substituent group in the ring structure thereof, thealiphatic cyclic group is preferably a polycyclic group, more preferablya group in which one or more hydrogen atoms have been removed from apolycycloalkane, and a group in which one or more hydrogen atoms havebeen removed from adamantane is particularly desirable.

When the aliphatic cyclic group contains a hetero atom-containingsubstituent group in the ring structure thereof, the heteroatom-containing substituent group is preferably —O—, —C(═O)—O—, —S—,—S(═O)₂— or —S(═O)₂—O—. Specific examples of such aliphatic cyclicgroups include groups represented by formulas (L1) to (L6) and (S1) to(S4) shown below.

In the formula, Q″ represents an alkylene group of 1 to 5 carbon atoms,—O—, —S—, —O—R⁹⁴— or —S—R⁹⁵— (wherein each of R⁹⁴ and R⁹⁵ independentlyrepresents an alkylene group of 1 to 5 carbon atoms); and m represents 0or 1.

As the alkylene group for Q″, R⁹⁴ and R⁹⁵, the same alkylene groups asthose described above for R⁹¹ to R⁹³ can be used.

In these aliphatic cyclic groups, part of the hydrogen atoms bonded tothe carbon atoms constituting the ring structure may be substituted witha substituent. Examples of substituents include an alkyl group, analkoxy group, a halogen atom, a halogenated alkyl group, a hydroxylgroup and an oxygen atom (═O).

As the alkyl group, an alkyl group of 1 to 5 carbon atoms is preferable,and a methyl group, an ethyl group, a propyl group, an n-butyl group ora tert-butyl group is particularly desirable.

As the alkoxy group and the halogen atom, the same groups as thesubstituent groups for substituting part or all of the hydrogen atomscan be used.

In the present invention, as X, a cyclic group which may have asubstituent is preferable. The cyclic group may be either an aromatichydrocarbon group which may have a substituent, or an aliphatic cyclicgroup which may have a substituent, and an aliphatic cyclic group whichmay have a substituent is preferable.

As the aromatic hydrocarbon group, a naphthyl group which may have asubstituent, or a phenyl group which may have a substituent ispreferable.

As the aliphatic cyclic group which may have a substituent, an aliphaticpolycyclic group which may have a substituent is preferable. As thealiphatic polycyclic group, the aforementioned group in which one ormore hydrogen atoms have been removed from a polycycloalkane, and groupsrepresented by the aforementioned formulas (L2) to (L6), (S3) and (S4)are preferable.

In the present invention, R⁴″ preferably has X-Q¹- as a substituent. Insuch a case, R⁴″ is preferably a group represented by the formulaX-Q¹-Y¹— (in the formula, Q¹ and X are the same as defined above; and Y¹represents an alkylene group of 1 to 4 carbon atoms which may have asubstituent, or a fluorinated alkylene group of 1 to 4 carbon atomswhich may have a substituent).

In the group represented by the formula X-Q¹-Y¹—, as the alkylene groupfor Y¹, the same alkylene group as those described above for Q¹ in whichthe number of carbon atoms is 1 to 4 can be used.

As the fluorinated alkylene group, the aforementioned alkylene group inwhich part or all of the hydrogen atoms has been substituted withfluorine atoms can be used.

Specific examples of Y¹ include —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂—,—CF(CF₃)CF₂—, —CF(CF₂CF₃)—, —C(CF₃)₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—,—CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—,—CF(CF₂CF₂CF₃)—, —C(CF₃)(CF₂CF₃)—; —CHF—, —CH₂CF₂—, —CH₂CH₂CF₂—,—CH₂CF₂CF₂—, —CH(CF₃)CH₂—, —CH(CF₂CF₃)—, —C(CH₃)(CF₃)—, —CH₂CH₂CH₂CF₂—,—CH₂CH₂CF₂CF₂—, —CH(CF₃)CH₂CH₂—, —CH₂CH(CF₃)CH₂—, —CH(CF₃)CH(CF₃)—,—C(CF₃)₂CH₂—; —CH₂—, —CH₂CH₂—, —CH₂CH₂CH₂—, —CH(CH₃)CH₂—, —CH(CH₂CH₃)—,—C(CH₃)₂—, —CH₂CH₂CH₂CH₂—, —CH(CH₃)CH₂CH₂—, —CH₂CH(CH₃)CH₂—,—CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, —CH(CH₂CH₂CH₃)—, and—C(CH₃)(CH₂CH₃)—.

Y¹ is preferably a fluorinated alkylene group, and particularlypreferably a fluorinated alkylene group in which the carbon atom bondedto the adjacent sulfur atom is fluorinated. Examples of such fluorinatedalkylene groups include —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—,—CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—,—C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—; —CH₂CF₂−, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—;—CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, and —CH₂CF₂CF₂CF₂—.

Of these, —CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂— or CH₂CF₂CF₂— is preferable,—CF₂—, —CF₂CF₂— or —CF₂CF₂CF₂— is more preferable, and —CF₂— isparticularly desirable.

The alkylene group or fluorinated alkylene group may have a substituent.The alkylene group or fluorinated alkylene group “has a substituent”means that part or all of the hydrogen atoms or fluorine atoms in thealkylene group or fluorinated alkylene group has been substituted withgroups other than hydrogen atoms and fluorine atoms.

Examples of substituents which the alkylene group or fluorinatedalkylene group may have include an alkyl group of 1 to 4 carbon atoms,an alkoxy group of 1 to 4 carbon atoms, and a hydroxyl group.

In formula (b-2), R⁵″ and R⁶″ each independently represent an aryl groupor alkyl group. At least one of R⁵″ and R⁶″ represents an aryl group. Itis preferable that both of R⁵″ and R⁶″ represent an aryl group.

As the aryl group for R⁵″ and R⁶″, the same aryl groups as thosedescribed above for R¹″ to R³″ can be used.

As the alkyl group for R⁵″ and R⁶″, the same alkyl groups as thosedescribed above for R¹″ to R³″ can be used.

It is particularly desirable that both of R⁵″ and R⁶″ represents aphenyl group.

As R⁴″ in formula (b-2), the same groups as those mentioned above forR⁴″ in formula (b-1) can be used.

Specific examples of suitable onium salt acid generators represented byformula (b-1) or (b-2) include diphenyliodoniumtrifluoromethanesulfonate or nonafluorobutanesulfonate;bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate ornonafluorobutanesulfonate; triphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;tri(4-methylphenyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;dimethyl(4-hydroxynaphthyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;monophenyldimethylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;diphenylmonomethylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;(4-methylphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;tri(4-tert-butyl)phenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;diphenyl(1-(4-methoxy)naphthyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;di(1-naphthyl)phenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-phenyltetrahydrothiophenium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-(4-methylphenyl)tetrahydrothiophenium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate;1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-methoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-ethoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiopheniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; 1-phenyltetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; 1-(4-hydroxyphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate;1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate; and 1-(4-methylphenyl)tetrahydrothiopyraniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate.

It is also possible to use onium salts in which the anion moiety ofthese onium salts is replaced by an alkyl sulfonate, such asmethanesulfonate, n-propanesulfonate, n-butanesulfonate,n-octanesulfonate, 1-adamantanesulfonate, 2-norbornanesulfonate ord-camphor-10-sulfonate; or replaced by an aromatic sulfonate, such asbenzenesulfonate, perfluorobenzenesulfonate or p-toluenesulfonate.

Furthermore, onium salts in which the anion moiety of these onium saltsare replaced by an anion moiety represented by any one of formulas (b1)to (b8) shown below can be used.

In the formulas, p represents an integer of 1 to 3; each of q1 and q2independently represents an integer of 1 to 5; q3 represents an integerof 1 to 12; t3 represents an integer of 1 to 3; each of r1 and r2independently represents an integer of 0 to 3; g represents an integerof 1 to 20; R⁷ represents a substituent; each of n1 to n5 independentlyrepresents 0 or 1; each of v0 to v5 independently represents an integerof 0 to 3; each of w1 to w5 independently represents an integer of 0 to3; and Q″ is the same as defined above.

As the substituent for R⁷, the same groups as those which theaforementioned aliphatic hydrocarbon group or aromatic hydrocarbon groupfor X may have as a substituent can be used.

If there are two or more of the R⁷ group, as indicated by the values r1,r2, and w1 to w5, then the two or more of the R⁷ groups may be the sameor different from each other.

Further, onium salt-based acid generators in which the anion moiety ingeneral formula (b-1) or (b-2) is replaced by an anion moietyrepresented by general formula (b-3) or (b-4) shown below (the cationmoiety is the same as (b-1) or (b-2)) may be used.

In the formulas, X″ represents an alkylene group of 2 to 6 carbon atomsin which at least one hydrogen atom has been substituted with a fluorineatom; and each of Y″ and Z″ independently represents an alkyl group of 1to 10 carbon atoms in which at least one hydrogen atom has beensubstituted with a fluorine atom.

X″ represents a linear or branched alkylene group in which at least onehydrogen atom has been substituted with a fluorine atom, and thealkylene group has 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms,and most preferably 3 carbon atoms.

Each of Y″ and Z″ independently represents a linear or branched alkylgroup in which at least one hydrogen atom has been substituted with afluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably1 to 7 carbon atoms, and most preferably 1 to 3 carbon atoms.

The smaller the number of carbon atoms of the alkylene group for X″ orthose of the alkyl group for Y″ and Z″ within the above-mentioned rangeof the number of carbon atoms, the more the solubility in a resistsolvent is improved.

Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″,it is preferable that the number of hydrogen atoms substituted withfluorine atoms is as large as possible because the acid strengthincreases and the transparency to high energy radiation of 200 nm orless or electron beam is improved.

The fluorination ratio of the alkylene group or alkyl group ispreferably from 70 to 100%, more preferably from 90 to 100%, and it isparticularly desirable that the alkylene group or alkyl group be aperfluoroalkylene group or perfluoroalkyl group in which all hydrogenatoms are substituted with fluorine atoms.

Furthermore, as an onium salt-based acid generator, a sulfonium salthaving a cation moiety represented by general formula (b-5) or (b-6)shown below may be used.

In formulas (b-5) and (b-6) above, each of R⁴¹ to R⁴⁶ independentlyrepresents an alkyl group, an acetyl group, an alkoxy group, a carboxygroup, a hydroxyl group or a hydroxyalkyl group; each of n₁ to n₅independently represents an integer of 0 to 3; and n₆ represents aninteger of 0 to 2.

With respect to R⁴¹ to R⁴⁶, the alkyl group is preferably an alkyl groupof 1 to 5 carbon atoms, more preferably a linear or branched alkylgroup, and most preferably a methyl group, ethyl group, propyl group,isopropyl group, n-butyl group or tert-butyl group.

The alkoxy group is preferably an alkoxy group of 1 to 5 carbon atoms,more preferably a linear or branched alkoxy group, and most preferably amethoxy group or an ethoxy group.

The hydroxyalkyl group is preferably the aforementioned alkyl group inwhich one or more hydrogen atoms have been substituted with hydroxygroups, and examples thereof include a hydroxymethyl group, ahydroxyethyl group and a hydroxypropyl group.

If there are two or more of an individual R⁴¹ to R⁴⁶ group, as indicatedby the corresponding value of n₁ to n₆, then the two or more of theindividual R⁴¹ to R⁴⁶ group may be the same or different from eachother.

n₁ is preferably 0 to 2, more preferably 0 or 1, and still morepreferably 0.

It is preferable that n₂ and n₃ each independently represent 0 or 1, andmore preferably 0.

n₄ is preferably 0 to 2, and more preferably 0 or 1.

n₅ is preferably 0 or 1, and more preferably 0.

n₆ is preferably 0 or 1, and more preferably 1.

The anion moiety of the sulfonium salt having a cation moietyrepresented by general formula (b-5) or (b-6) is not particularlylimited, and the same anion moieties for onium salt-based acidgenerators which have been proposed may be used. Examples of such anionmoieties include fluorinated alkylsulfonic acid ions such as anionmoieties (R⁴″SO₃ ⁻) for onium salt-based acid generators represented bygeneral formula (b-1) or (b-2) shown above; and anion moietiesrepresented by general formula (b-3) or (b-4) shown above.

In the present description, an oximesulfonate-based acid generator is acompound having at least one group represented by general formula (B-1)shown below, and has a feature of generating acid by irradiation. Suchoximesulfonate acid generators are widely used for a chemicallyamplified resist composition, and can be appropriately selected.

In the formula, each of R³¹ and R³² independently represents an organicgroup.

The organic group for R³¹ and R³² refers to a group containing a carbonatom, and may include atoms other than carbon atoms (e.g., a hydrogenatom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom(such as a fluorine atom and a chlorine atom) and the like).

As the organic group for R³¹, a linear, branched, or cyclic alkyl groupor aryl group is preferable. The alkyl group or the aryl group may havea substituent. The substituent is not particularly limited, and examplesthereof include a fluorine atom and a linear, branched, or cyclic alkylgroup having 1 to 6 carbon atoms. The alkyl group or the aryl group “hasa substituent” means that part or all of the hydrogen atoms of the alkylgroup or the aryl group is substituted with a substituent.

The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1to 10 carbon atoms, still more preferably 1 to 8 carbon atoms, stillmore preferably 1 to 6 carbon atoms, and most preferably 1 to 4 carbonatoms. As the alkyl group, a partially or completely halogenated alkylgroup (hereinafter, sometimes referred to as a “halogenated alkylgroup”) is particularly desirable. The “partially halogenated alkylgroup” refers to an alkyl group in which part of the hydrogen atoms aresubstituted with halogen atoms and the “completely halogenated alkylgroup” refers to an alkyl group in which all of the hydrogen atoms aresubstituted with halogen atoms. Examples of halogen atoms includefluorine atoms, chlorine atoms, bromine atoms and iodine atoms, andfluorine atoms are particularly desirable. In other words, thehalogenated alkyl group is preferably a fluorinated alkyl group.

The aryl group preferably has 4 to 20 carbon atoms, more preferably 4 to10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the arylgroup, partially or completely halogenated aryl group is particularlydesirable. The “partially halogenated aryl group” refers to an arylgroup in which some of the hydrogen atoms are substituted with halogenatoms and the “completely halogenated aryl group” refers to an arylgroup in which all of hydrogen atoms are substituted with halogen atoms.

As R³¹, an alkyl group of 1 to 4 carbon atoms which has no substituentor a fluorinated alkyl group of 1 to 4 carbon atoms is particularlydesirable.

As the organic group for R³², a linear, branched, or cyclic alkyl group,aryl group, or cyano group is preferable. Examples of the alkyl groupand the aryl group for R³² include the same alkyl groups and aryl groupsas those described above for R³¹.

As R³², a cyano group, an alkyl group of 1 to 8 carbon atoms having nosubstituent or a fluorinated alkyl group of 1 to 8 carbon atoms isparticularly desirable.

Preferred examples of the oxime sulfonate acid generator includecompounds represented by general formula (B-2) or (B-3) shown below.

In the formula, R³³ represents a cyano group, an alkyl group having nosubstituent or a halogenated alkyl group; R³⁴ represents an aryl group;and R³⁵ represents an alkyl group having no substituent or a halogenatedalkyl group.

In the formula, R³⁶ represents a cyano group, an alkyl group having nosubstituent or a halogenated alkyl group; R³⁷ represents a divalent ortrivalent aromatic hydrocarbon group; R³⁸ represents an alkyl grouphaving no substituent or a halogenated alkyl group; and p″ represents 2or 3.

In general formula (B-2), the alkyl group having no substituent or thehalogenated alkyl group for R³³ preferably has 1 to 10 carbon atoms,more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbonatoms.

As R³³, a halogenated alkyl group is preferable, and a fluorinated alkylgroup is more preferable.

The fluorinated alkyl group for R³³ preferably has 50% or more of thehydrogen atoms thereof fluorinated, more preferably 70% or more, andmost preferably 90% or more.

Examples of the aryl group for R³⁴ include groups in which one hydrogenatom has been removed from an aromatic hydrocarbon ring, such as aphenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, ananthryl group, and a phenanthryl group, and heteroaryl groups in whichsome of the carbon atoms constituting the ring(s) of these groups aresubstituted with hetero atoms such as an oxygen atom, a sulfur atom, anda nitrogen atom. Of these, a fluorenyl group is preferable.

The aryl group for R³⁴ may have a substituent such as an alkyl group of1 to 10 carbon atoms, a halogenated alkyl group, or an alkoxy group. Thealkyl group and halogenated alkyl group as the substituent preferablyhas 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms.Further, the halogenated alkyl group is preferably a fluorinated alkylgroup.

The alkyl group having no substituent or the halogenated alkyl group forR³⁵ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbonatoms, and most preferably 1 to 6 carbon atoms.

As R³⁵, a halogenated alkyl group is preferable, and a fluorinated alkylgroup is more preferable.

In terms of enhancing the strength of the acid generated, thefluorinated alkyl group for R³⁵ preferably has 50% or more of thehydrogen atoms fluorinated, more preferably 70% or more, still morepreferably 90% or more. A completely fluorinated alkyl group in which100% of the hydrogen atoms are substituted with fluorine atoms isparticularly desirable.

In general formula (B-3), as the alkyl group having no substituent andthe halogenated alkyl group for R³⁶, the same alkyl group having nosubstituent and the halogenated alkyl group described above for R³³ canbe used.

Examples of the divalent or trivalent aromatic hydrocarbon group for R³⁷include groups in which one or two hydrogen atoms have been removed fromthe aryl group for R³⁴.

As the alkyl group having no substituent or the halogenated alkyl groupfor R³⁸, the same one as the alkyl group having no substituent or thehalogenated alkyl group for R³⁵ can be used.

p″ is preferably 2.

Specific examples of suitable oxime sulfonate acid generators includeα-(p-toluenesulfonyloxyimino)-benzyl cyanide,α-(p-chlorobenzenesulfonyloxyimino)-benzyl cyanide,α-(4-nitrobenzenesulfonyloxyimino)-benzyl cyanide,α-(4-nitro-2-trifluoromethylbenzenesulfonyloxyimino)-benzyl cyanide,α-(benzenesulfonyloxyimino)-4-chlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-2,4-dichlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-2,6-dichlorobenzyl cyanide,α-(benzenesulfonyloxyimino)-4-methoxybenzyl cyanide,α-(2-chlorobenzenesulfonyloxyimino)-4-methoxybenzyl cyanide,α-(benzenesulfonyloxyimino)-thien-2-yl acetonitrile,α-(4-dodecylbenzenesulfonyloxyimino)benzyl cyanide,α-[(p-toluenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,α-[(dodecylbenzenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,α-(tosyloxyimino)-4-thienyl cyanide,α-(methylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cycloheptenyl acetonitrile,α-(methylsulfonyloxyimino)-1-cyclooctenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-cyclohexyl acetonitrile,α-(ethylsulfonyloxyimino)-ethyl acetonitrile,α-(propylsulfonyloxyimino)-propyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-cyclopentyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-cyclohexyl acetonitrile,α-(cyclohexylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(ethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(isopropylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(n-butylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,α-(ethylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(isopropylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(n-butylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,α-(methylsulfonyloxyimino)-phenyl acetonitrile,α-(methylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-phenyl acetonitrile,α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(ethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,α-(propylsulfonyloxyimino)-p-methylphenyl acetonitrile, andα-(methylsulfonyloxyimino)-p-bromophenyl acetonitrile.

Further, oxime sulfonate acid generators disclosed in JapaneseUnexamined Patent Application, First Publication No. Hei 9-208554(Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) andoxime sulfonate acid generators disclosed in WO 2004/074242A2 (Examples1 to 40 described at pages 65 to 86) may be preferably used.

Furthermore, as preferable examples, the following can be used.

Of the aforementioned diazomethane acid generators, specific examples ofsuitable bisalkyl or bisaryl sulfonyl diazomethanes includebis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane, andbis(2,4-dimethylphenylsulfonyl)diazomethane.

Further, diazomethane acid generators disclosed in Japanese UnexaminedPatent Application, First Publication No. Hei 11-035551, JapaneseUnexamined Patent Application, First Publication No. Hei 11-035552 andJapanese Unexamined Patent Application, First Publication No. Hei11-035573 may be preferably used.

Furthermore, as examples of poly(bis-sulfonyl)diazomethanes, thosedisclosed in Japanese Unexamined Patent Application, First PublicationNo. Hei 11-322707, including1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane,1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane,1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane,1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane,1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane,1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane,1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be given.

As the component (B), one type of acid generator may be used, or two ormore types of acid generators may be used in combination.

In the present invention, as the component (B), it is preferable to useat least an onium salt acid generator having a fluorinatedalkylsulfonate ion as an anion moiety, and it is more preferable to usea combination of an onium salt acid generator having an anionrepresented by any of the aforementioned formulas (b1) to (b8) and anonium salt acid generator having an anion represented by theaforementioned formula (b-3).

In the resist composition used in the present invention, the amount ofthe component (B) relative to 100 parts by weight of the component (A)is preferably 0.5 to 50 parts by weight, and more preferably 1 to 40parts by weight. When the amount of the component (B) is within theabove-mentioned range, formation of a resist pattern can besatisfactorily performed. Further, by virtue of the above-mentionedrange, a uniform solution can be obtained and the storage stabilitybecomes satisfactory.

<Optional Components>

[Component (D)]

It is preferable that the resist composition used in the presentinvention further includes a nitrogen-containing organic compound (D)(hereafter referred to as the component (D)) as an optional component.

As the component (D), there is no particular limitation as long as itfunctions as an acid diffusion control agent, i.e., a quencher whichtraps the acid generated from the component (B) upon exposure. Amultitude of these components (D) have already been proposed, and any ofthese known compounds may be used. Among these, an aliphatic amine,particularly a secondary aliphatic amine or tertiary aliphatic amine ispreferable.

An aliphatic amine is an amine having one or more aliphatic groups, andthe aliphatic groups preferably have 1 to 12 carbon atoms.

Examples of these aliphatic amines include amines in which at least onehydrogen atom of ammonia (NH₃) has been substituted with an alkyl groupor hydroxyalkyl group of no more than 12 carbon atoms (i.e., alkylaminesor alkylalcoholamines), and cyclic amines.

Specific examples of alkylamines and alkylalcoholamines includemonoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine,n-nonylamine, and n-decylamine; dialkylamines such as diethylamine,di-n-propylamine, di-n-heptylamine, di-n-octylamine, anddicyclohexylamine; trialkylamines such as trimethylamine, triethylamine,tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine,tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine,tri-n-nonylamine, tri-n-decylamine, and tri-n-dodecylamine; and alkylalcohol amines such as diethanolamine, triethanolamine,diisopropanolamine, triisopropanolamine, di-n-octanolamine, andtri-n-octanolamine. Among these, trialkylamines of 5 to 10 carbon atomsare preferable, and tri-n-pentylamine and tri-n-octylamine areparticularly desirable.

Examples of the cyclic amine include heterocyclic compounds containing anitrogen atom as a hetero atom. The heterocyclic compound may be amonocyclic compound (aliphatic monocyclic amine), or a polycycliccompound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine,and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, andspecific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene,1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines includetris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine,tris{2-(2-methoxyethoxymethoxy)ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)ethyl}amine,tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine and triethanolaminetriacetate, and triethanolamine triacetate is preferable.

Further, as the component (D), an aromatic amine may be used.

Examples of aromatic amines include aniline, pyridine,4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole andderivatives thereof, as well as diphenylamine, triphenylamine,tribenzylamine, 2,6-diisopropylaniline andN-tert-butoxycarbonylpyrrolidine.

As the component (D), one type of compound may be used alone, or two ormore types may be used in combination.

The component (D) is typically used in an amount within a range from0.01 to 5.0 parts by weight, relative to 100 parts by weight of thecomponent (A). When the amount of the component (D) is within theabove-mentioned range, the shape of the resist pattern and the postexposure stability of the latent image formed by the pattern-wiseexposure of the resist layer are improved.

<Component (E)>

Furthermore, in the resist composition, for preventing any deteriorationin sensitivity, and improving the resist pattern shape and the postexposure stability of the latent image formed by the pattern-wiseexposure of the resist layer, at least one compound (E) (hereafterreferred to as the component (E)) selected from the group consisting ofan organic carboxylic acid, or a phosphorus oxo acid or derivativethereof can be added as an optional component.

Examples of suitable organic carboxylic acids include acetic acid,malonic acid, citric acid, malic acid, succinic acid, benzoic acid, andsalicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonicacid and phosphinic acid. Among these, phosphonic acid is particularlydesirable.

Examples of oxo acid derivatives include esters in which a hydrogen atomwithin the above-mentioned oxo acids is substituted with a hydrocarbongroup. Examples of the hydrocarbon group include an alkyl group of 1 to5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esterssuch as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esterssuch as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonicacid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esterssuch as phenylphosphinic acid.

As the component (E), one type may be used alone, or two or more typesmay be used in combination.

As the component (E), an organic carboxylic acid is preferred, andsalicylic acid is particularly desirable.

In the present invention, when the resist composition contains thecomponent (E), the amount of the component (E) is used in an amountwithin a range from 0.01 to 5.0 parts by weight, relative to 100 partsby weight of the component (A).

<Component (F)>

The resist composition may further include a fluorine additive(hereafter, referred to as “component (F)”) for imparting waterrepellency to the resist film. As the component (F), for example, afluorine-containing polymeric compound described in Japanese UnexaminedPatent Application, First Publication No. 2010-002870.

Specific examples of the component (F) include copolymers having astructural unit represented by formula (f1) shown below. The component(F) is preferably a polymer (homopolymer) consisting of a structuralunit represented by formula (f1) shown below; a copolymer of astructural unit represented by formula (f1) shown below and theaforementioned structural unit (a1); or a copolymer of a structural unitrepresented by formula (f1) shown below, a structural unit derived fromacrylic acid or methacrylic acid and the aforementioned structural unit(a1). As the structural unit (a1) to be copolymerized with a structuralunit represented by formula (f1) shown below, a structural unitrepresented by the aforementioned formula (a1-5) is preferable, and astructural unit represented by the aforementioned formula (a11-1-1) isparticularly desirable.

In the formula, R is the same as defined above; a1 represents an integerof 1 to 5; and R²″ represents an organic group containing a fluorineatom.

In formula (f1), R is the same as defined above. As R, a hydrogen atomor a methyl group is preferable.

In formula (f1), a1 represents an integer of 1 to 5, preferably aninteger of 1 to 3, and more preferably 1 or 2.

In formula (f1), R²″ represents an organic group containing a fluorineatom, and is preferably a hydrocarbon group containing a fluorine atom.

The hydrocarbon group containing a fluorine atom may be linear, branchedor cyclic, and preferably has 1 to 20 carbon atoms, more preferably 1 to15 carbon atoms, and most preferably 1 to 10 carbon atoms.

It is preferable that the hydrocarbon group having a fluorine atom has25% or more of the hydrogen atoms within the hydrocarbon groupfluorinated, more preferably 50% or more, and most preferably 60% ormore, as the hydrophobicity of the resist film during immersion exposureis enhanced.

Among these, as R²″, a fluorinated hydrocarbon group of 1 to 5 carbonatoms is preferable, and a methyl group, —CH₂—CF₃, —CH₂—CF₂—CF₃,—CH(CF₃)₂, —CH₂—CH₂—CF₃, and —CH₂—CH₂—CF₂—CF₂—CF₂—CF₃ are mostpreferable.

As the component (F), one type may be used alone, or two or more typesmay be used in combination.

The component (F) is typically used in an amount within a range from 1to 10 parts by weight, relative to 100 parts by weight of the component(A).

If desired, other miscible additives can also be added to the resistcomposition. Examples of such miscible additives include additive resinsfor improving the performance of the resist film, surfactants forimproving the applicability, dissolution inhibitors, plasticizers,stabilizers, colorants, halation prevention agents, and dyes.

If desired, other miscible additives can also be added to the resistcomposition. Examples of such miscible additives include additive resinsfor improving the performance of the resist film, surfactants forimproving the applicability, dissolution inhibitors, plasticizers,stabilizers, colorants, halation prevention agents, and dyes.

<Component (S)>

The resist composition can be produced by dissolving the materials forthe resist composition in an organic solvent (hereafter, referred to as“component (S)”).

The component (S) may be any organic solvent which can dissolve therespective components to give a uniform solution, and one or more kindsof any organic solvent can be appropriately selected from those whichhave been conventionally known as solvents for a chemically amplifiedresist.

Examples of the component (S) include lactones such as γ-butyrolactone;ketones such as acetone, methyl ethyl ketone, cyclohexanone,methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone;polyhydric alcohols, such as ethylene glycol, diethylene glycol,propylene glycol and dipropylene glycol; compounds having an ester bond,such as ethylene glycol monoacetate, diethylene glycol monoacetate,propylene glycol monoacetate, and dipropylene glycol monoacetate;polyhydric alcohol derivatives including compounds having an ether bond,such as a monoalkylether (e.g., monomethylether, monoethylether,monopropylether or monobutylether) or monophenylether of any of thesepolyhydric alcohols or compounds having an ester bond (among these,propylene glycol monomethyl ether acetate (PGMEA) and propylene glycolmonomethyl ether (PGME) are preferable); cyclic ethers such as dioxane;esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethylacetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, and ethyl ethoxypropionate; and aromatic organicsolvents such as anisole, ethylbenzylether, cresylmethylether,diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene,diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymeneand mesitylene.

The component (S) can be used individually, or in combination as a mixedsolvent.

Among these, γ-butyrolactone, propylene glycol monomethyl ether acetate(PGMEA), propylene glycol monomethyl ether (PGME) and ethyl lactate (EL)are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixingPGMEA with a polar solvent is preferable. The mixing ratio (weightratio) of the mixed solvent can be appropriately determined, taking intoconsideration the compatibility of the PGMEA with the polar solvent, butis preferably in the range of 1:9 to 9:1, more preferably from 2:8 to8:2.

Specifically, when EL is mixed as the polar solvent, the PGMEA:EL weightratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to8:2. Alternatively, when PGME is mixed as the polar solvent, thePGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferablyfrom 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of at least one of PGMEAand EL with γ-butyrolactone is also preferable. The mixing ratio(former:latter) of such a mixed solvent is preferably from 70:30 to95:5.

Furthermore, as the component (S), a mixed solvent of PGMEA andcyclohexanone is also preferable. The mixing ratio of such a mixedsolvent is preferably PGMEA:cyclohexanone=95 to 5:10 to 90.

According to the present invention, miniaturization of the patterndimension can be achieved, and the uniformity of the pattern can beimproved.

As described above, in general, with respect to a resist pattern using anegative tone development resist composition, when narrowing down of theintervals between patterns (e.g., the diameter of hole in a contact holepattern, the space width in the case of a space (trench) pattern) isattempted by heat shrinking, the intervals between the patterns arerather increased. The reason for this is that, in a resist film formedusing a general negative tone development resist composition, thepattern portions have a gap generated inside thereof as result ofelimination of groups, so that the pattern portions shrink toward thegaps.

On the other hand, by the method of forming a resist pattern accordingto the present invention, a thermal treatment is conducted aftercovering the resist pattern formed using a negative tone developmentresist composition with a coating film of a coating material. As aresult, the coating film itself can be subjected to heat shrinking, andit is presumed that the side walls of the pattern portions of the resistfilm can be pulled toward the space between the patterns, therebyobtaining the above effects.

EXAMPLES

As follows is a description of examples of the present invention,although the scope of the present invention is by no way limited bythese examples.

Examples 1 to 3 Comparative Example 1

The components shown in Table 1 were mixed together to obtain negativetone development resist compositions.

TABLE 1 Component Component Component (A) Component (B) (F) (S) Ex. 1(A)-1 (B)-1 (B)-2 (F)-1 (S)-1/(S)-2 Comp. Ex. 1 [100] [6.5] [4.2] [4.0][2500/280] Ex. 2 (A)-2 (B)-3 (B)-2 (F)-1 (S)-1/(S)-2 [100] [20]   [4.2][4.0] [2500/280]

In Table 1, the reference characters indicate the following. Further,the values in brackets [ ] indicate the amount (in terms of parts byweight) of the component added.

(A)-1: polymeric compound (A)-1 shown below [Mw=8,000, Mw/Mn=1.56,l/m/n/o=45/35/10/10 (molar ratio)]

(A)-2: polymeric compound (A)-2 shown below [Mw=8,000, Mw/Mn=1.57,l/m/n/o/p=45/30/9/8/8 (molar ratio)]

(B)-1: compound (B)-1 shown below

(B)-2: compound (B)-2 shown below

(B)-3: compound (B)-3 shown below

(F)-1: polymeric compound (F)-1 shown below [Mw=25,000, Mw/Mn=1.61,l/m=30/70 (molar ratio)]

(S)-1: propyleneglycol monomethyletheracetate

(S)-2: cyclohexanone

Using the obtained negative tone development resist compositions, resistpatterns were formed in the following manner.

Formation of Resist Pattern 1 Examples 1 and 2, Comparative Example 1

An organic anti-reflection film composition (product name: ARC95,manufactured by Brewer Science Ltd.) was applied to an 12-inch siliconwafer using a spinner, and the composition was then baked at 205° C. for60 seconds, thereby forming an organic anti-reflection film having afilm thickness of 90 nm.

Then, the resist composition of each example was applied to the organicanti-reflection film using a spinner, and was then prebaked (PAB) on ahotplate at 105° C. for 60 seconds and dried, thereby forming a resistfilm having a film thickness of 100 nm.

Subsequently, the resist film was selectively irradiated with an ArFexcimer laser (193 nm) through a mask, using an ArF exposure apparatusNSR-S60913 (manufactured by Nikon Corporation, NA (numericalaperture)=1.07, Crosspole (0.78/0.97) w/POLANO).

Next, PEB was conducted at 110° C. for 60 seconds, and developmenttreatment was performed at 23° C. for 13 seconds using butyl acetate,followed by drying by shaking. As a result, a contact hole pattern (CHpattern) in which holes having a diameter of 50 nm were equally spaced(pitch: 100 nm) was formed. The optimum exposure dose Eop was 26 mJ/cm².

Subsequently, to each of the CH patterns obtained in Examples 1 and 2, acoating material containing a copolymer of acrylic acid andvinylpyrrolidone (acrylic acid:vinylpyrrolidone=2:1 (weight ratio)),triethylamine, a surfactant and water and exhibiting a pH of 3 wasapplied using a spinner, thereby forming a coating film having athickness of 200 nm as measured from the substrate.

On the other hand, a coating film was not formed on the CH pattern ofComparative Example 1.

Thereafter, the CH pattern on the substrate was subjected to a thermaltreatment at a temperature of 100° C. (reference), 140° C., 150° C.,155° C. or 160° C., followed by removing the coating film at 23° C.using pure water.

The sizes (hole diameters) of the CH pattern after being subjected tothe thermal treatment at each temperature are shown in Table 2.

Further, with respect to the CH pattern subjected to the thermaltreatment at each temperature, the diameters of 200 holes were measured.From the results, the value of 3 times the standard deviation wascalculated as a yardstick of CDU (CD uniformity; pattern uniformity).The smaller the value is, the better the CDU. The results are shown inTable 2.

Formation of Resist Pattern 2 Example 3

Evaluations were performed in the same manner as in Example 1, exceptthat the pH of the coating material used was adjusted to 7 (the amountof triethylamine was adjusted). The results are shown in Table 2.

TABLE 2 100° 140° 150° 155° 160° C. (Ref.) C. C. C. C. Ex. 1 Hole 50.046.4 45.0 45.3 42.6 diameter (nm) CDU 8.4 7.4 7.5 6.9 7.4 Ex. 2 Hole50.1 48.5 46.8 46.2 45.2 diameter (nm) CDU 7.8 7.3 7.2 6.8 6.7 Ex. 3Hole 50.0 47.5 46.9 46.8 46.6 diameter (nm) CDU 8.4 8.0 7.8 7.5 7.4Comp. Ex. 1 Hole 50.0 51.0 51.8 — 52.4 diameter (nm) CDU 8.4 7.9 10.4 —7.6

From the results shown above, the resist patterns formed by the methodof Examples 1 to 3 had a small pattern size and exhibited excellentpattern uniformity, as compared to the resist pattern formed by themethod of Comparative Example 1.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

What is claimed is:
 1. A method of forming a resist pattern, comprising:a step of forming a resist film on a substrate using a resistcomposition comprising a base component (A) which exhibits decreasedsolubility in an organic solvent under action of acid and anacid-generator component (B) which generates acid upon exposure; a stepof subjecting the resist film to exposure; a step of patterning theresist film by a negative-tone development using a developing solutioncontaining the organic solvent to form a resist pattern; a step ofapplying a coating material to the resist pattern, thereby forming acoating film; a step of performing a thermal treatment at a temperaturelower than the softening point of the resist pattern, thereby heatshrinking the coating film to narrow an interval between the resistpattern; and a step of removing the coating film, wherein the pH of thecoating material is 1 to
 5. 2. The method according to claim 1, whereinthe coating material comprises an aqueous polymer.
 3. The methodaccording to claim 2, wherein the aqueous polymer comprises at least onemember selected from the group consisting of alkylene glycol polymers,cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers,epoxy polymers, melamine polymers and nylon polymers.
 4. The methodaccording to claim 1, wherein the coating material further comprises anaqueous amine.